Mobile vs Immobile Nutrients

Fig. 1   Older leaves on celery turning yellow while the growing points in the center remain green.

The last time I looked there were seventeen known essential elements for plants.  Each element performs a specific function.  When conditions are at optimum levels we see a healthy plant, but when one or more element is deficient we see a "needy" plant.  To determine which of these various elements is lacking, one has to begin by understanding where the plant stores all its limited reserves.  Some elements are like cash - they can be used anywhere, while some are like gift cards - which can only be spent in specific stores.  Plant nutrients are either plant-mobile or plant-immobile.   Understanding these two characteristics is important because it helps gardeners interpret deficiency symptoms more accurately.

What are plant-mobile nutrients?

Plant-mobile nutrients are those that are capable of being translocated within the plant.  When a plant is deficient of these elements, the nutrient that is already within the plant will be transported to where it is needed most - the young tissues.  Deficiency symptoms of plant-mobile elements are observed on the older leaves first.  One example of a plant-mobile nutrient is nitrogen.  If nitrogen is deficient in a plant, older leaves would turn yellowish first while the newer leaves remain relatively green (Fig. 1). The plant directs the nutrient where it is most needed to prolong the life of the stressed plant.

Examples of plant mobile nutrients are nitrogen (N), phosphorous (P), and potassium (K).  Manganese and sulfur are moderately mobile

What are plant-immobile nutrients?
By now, the answer to this question is obvious.  Plant-immobile nutrients  cannot be translocated from older tissue to a new one due to the nature of the elements and sometimes other conditions.  In other words they are stuck where ever they landed the first time.   They have reached their destination.  Deficiency symptoms for these elements are observed in the young plant parts.  Calcium is an example of plant-immobile elements.  It plays an important role in cell expansion.  When calcium is deficient, the young shoots and flower buds exhibit the devastating effects.  If the condition is not corrected the shoots and bud get aborted eventually.

Examples of plant-immobile nutrients are:  Iron (Fe), Calcium (Ca), Manganese (Mn), Zinc (Zn), Copper (Cu), and Boron (B). 

Plant nutrients are like humans.  Some are always moving to where the activity is going on while others just settle where they landed the first time until they go back to the ground. 

Guttation

Fig. 1   Droplets of water suspended on the tip of leaf blades.

Water is a key component of any life form. In every organism, water is constantly moving within the system as the transport vehicle for essential elements. Water molecules move around in response to both environmental and internal conditions.  In the case of plants when water is lacking, cells lose their turgor pressure and they behave in an austere mode - functioning to the minimum in order try to conserve all the remaining water within. On the contrary, when there is excess of water within and around the roots zone, plants behave in such a way that water is used up or released as fast as physiological processes allow. The plant system opens all water exits to the maximum because plant cells can only hold up to a certain amount of water before damage can occur. 

Fig. 2    Guttation:  Water is pushed out through hydathodes.

Excess Water. This topic is about a condition of excess water both in the soil and in the air.  Water gets absorbed by the roots and released through the leaves.  When the release-process is hindered by both sides of the system (by being saturated), the plant has to do something beyond ordinary. 

When you see your lawn in the morning glistening with drops of water suspended at the tip of every grass blade (Fig. 1 and Fig. 2),  you are seeing a case of guttation.  Guttation is simply the process when water from within the plant accumulates on the tips of the leaves.  However, in order to fully understand guttation, we need to contrast and compare aspects of this phenomenon with similar but not related occurrences.   

1.  The water droplet:  Is it the same as dew? 

During guttation, water droplets form at the apical margins of some grasses (Fig.1) or along the leaf margins of some dicots species (Fig. 3).   These droplets of water are different from dew.  Dew is the result of condensation of atmospheric moisture.  The whole surface of the leaves would be all wet.  As the temperature cools down at night and evaporation of molecules outside the leaf slows down or completely stops, root pressure builds up causing water to be pushed violently upwards in search of an exit. Guttation droplet (fluid) originates from within the plant.  Sometimes it is considered a xylem sap.  It is not pure water since it contains some amounts of minerals and sugars.

Guttation droplets form only around the leaf margin.  Dew forms on the leaf surface. 

Fig. 3  Guttation on young leaves of  a rose.

2.  The Passage Way:  Is it the Stomata? 

Some plant species are equipped with hydathodes.   Hydathodes are pore-like structures along the leaf margins that allow the exit of water from the plant in liquid form (Fig.3).  During photosynthesis, stomata open not only to allow carbon dioxide to get into the plant but it also allows the passage of water molecules.  The stomata allow the exit of water in gas form.  For that reason, although water is continuously exiting through the stomata, water is not visible on the leaf surface.  The water molecules join the atmospheric air immediately.   When the temperature is low (at night in particular), transpiration is dramatically decreased resulting in excess water in the plant system.  However this does not mean that water stops getting into the plant. 

Through osmosis, water moves from an area of weaker concentration to stronger concentration.   Because of the higher salt content of the plant sap, (difference in the salt content of the plant sap and soil moisture) water diffuses into the root xylem.   As a result, root pressure builds up - water rushes into the plant but with low temperatures, a traffic jam occurs at the stomata exit.  Fluids are then forced through the hydathodes and fluid comes out are tears along the leaf margins of some plants (Fig. 3). 

Guttation happens through a specialized structure called hydathodes.

3.  The Process:  Is it the same as transpiration? 

Transpiration is the process when the water molecules from the roots are lost into the surface of the leaves.   Imagine that inside the plant there are tiny capillary tubes, called xylem, that stretch from the roots to the leaves.  Then imagine that the tubes are filled with a single line of water molecules starting from right outside the root hair all the way up to the opening of the stomata by way of cohesion (the property of water molecules to attract the same molecules).  As the outer-most molecule escapes the stomata into the air, the next molecule takes its position and the rest follow leaving a new vacant position at the tip of the root.  So another  molecule gets in.  It's a cycle that goes on and on. There are two processes involved here:  transpiration (exit of water molecule from the stomata) and water absorption (entrance of water molecule into the plant).  Depending on the condition of the surrounding environment (temperature, relative humidity, wind velocity, light intensity) these stomata open and close to regulate transpiration.  For the plant, transpiration is an on-going process.

Guttation on the other hand is special-occasion process.  Certain uncommon conditions have to be met for guttation to occur.  Saturated soil and high soil temperature combined with high atmospheric humidity and low air temperature are the optimum conditions for guttation. This is  usually happens at night that is why we see the beads of water only in the morning.   Guttation happens only in specific plant species.  The process is only possible in plants that are equipped with enlarged specialized stomata called hydathodes.  I found an excellent picture of hydathodes in action - one can almost feel the movement of water through those openings.  The image is very helpful in understanding the process of guttation.


Guttation happens when there is excessive water in the soil and there is an absence of water loss through transpiration. 

Guttation is likely to occur during the night, hence the guttation droplets are seen in the mornings.

Adventitious Roots and Shoots on Kalanchoe panamensis

Fig. 1  Adventitious roots on Kalanchoe panamensis

Kalanchoe panamensis is a very interesting plant.  Depending on the surrounding moisture conditions, roots freely come out from the upper parts of their stems (Fig. 1).  Once these roots reach the ground they function as a regular root (for absorption) and as stilt roots (for plant support).  As the stem lodges, the plant anchors to the ground with these roots allowing each node to be anchored and independent.  This prepares each section of the plant for any eventual separation from the main stem.  This is what I call 'life insurance plan'. 

From the leaves, new shoots grow to become new plants (Fig. 2).  This is a common occurrence on the leaves that have fallen off the plant.  Even without gardener's intervention, the residual soil moisture underneath the leaves is sufficient to get the new sprouts get established.  With these characteristics, this plant has one mission - to clone itself for self-preservation.

Fig. 2   Adventitious shoots growing on a detached leaf  (Kalanchoe panamensis).

 

Adventitious Roots. The standard root system of a plant originates from the radicle in the seed. The radicle grows to become the primary root. From the primary roots grow lateral roots. As a general sequence, lateral roots always grow from roots. Roots beget roots. However, there is a specialized type of roots called adventitious roots that originates from unusual and unexpected parts on the plant. Adventitious roots form on stem or leaf-derived tissues.


Adventitious Shoots. The first shoot from a seed originates from the plumule which eventually grows into the primary stem. Then lateral buds grow from this main stem. However there is a shoot formation that takes place on root and leaf tissues (Fig. 2). This is called adventitious shoot formation because the shoot or buds grow where they are not expected to.

Adventitious root and shoot formation is the key phenomenon that leads to regeneration.  It is the same phenomenon makes tissue culture possible.  When a plant is stressed or injured or detached from the plant, the natural response of the plant cells is to start life all over again.  Where would cloning or asexual propagation be without these roots and buds that grow from unexpected origins?   It is unimaginable how we could have two plants that are genetically the same if plants were not capable of growing adventitious roots.


Many succulent plants clone themselves naturally like Kalanchoe panamensis. Some grow roots at the base of the leaves instead of the edges of the leaf blade such as Echeveria 'Black Prince' in Fig.3. You can probably name a few species that does exactly the same thing. The fact is that succulents thrive on less water. Some of them originated from places where environmental conditions may not permit the completion of their life cycle - meaning from seed to seed. However, they have been equipped (by the Creator) with the ability to reproduce themselves apart from the seeds. This ability is backed by adventitious root and adventitious shoot formation. As a result, we can get plants that are genetically identical over and over again. We can design gardens and plan on the exact full size, color, and flowering time of every plant we put in the ground - all because of adventitious roots and adventitious shoots.

Fig. 3  Adventitious roots on leaves of Echeveria 'Black Prince'.

Kalanchoe panamensis is just a visual aid to demonstrate what we often take for granted - the adventitious root and shoot formation. 

Can you name some plant species in your garden that clone themselves naturally?

Below the Soil Surface

Fig. 1  Volunteer potato plant.

Ever since I planted my first potato crop in my garden, volunteer potato plants became a normal occurrence every spring.  No matter how much I'd try to look for all the tubers at harvest time, there would always be some tubers left behind.   As a general rule, I rarely use the same area in my garden for the same crop two seasons in a row.  In other words, I practice crop rotation.  The result of this is that some of the weeds that I have to remove from my garden before planting my spring crops are volunteer-potatoes (Fig. 1).   Sometimes when I pull them out of the ground they already have new potatoes (small and immature tubers) which when boiled and buttered make a treat for my kids.

When I was pulling the volunteer potatoes, I saw one that I could use as a visual aid for something I'd like to talk about - the parts of a potato plant that directly affects its performance.

 

 Parts of a Potato Plant: Underground (Part One)

Fig. 2 Parts of a growing potato plant.

Mother tuber is the seed tuber that was planted and where the new crop has grown from.  My former professor, Peter Vander Zaag, used to say that when a healthy seed tuber is planted, it is likely that it will remain till harvest time as a mother tuber.   Why it is called a mother tuber-- I'm guessing that it is because it has had the chance to reproduce.  :)  A firm and healthy mother tuber at harvest time indicates that the early growing conditions of the crop was  favorable allowing the new plant to shift from being dependent (drawing energy from the mother plant), to independently producing energy (through photosynthesis) before the energy from the mother tuber is depleted.

The mother tuber in the picture (Fig. 2), being a volunteer potato, was situated close to the surface of the soil.  It was exposed to a larger array of pests as indicated by the presence of holes on  the tuber. 

Fig. 3.    Stolons develop underground; lateral stems develop above ground. 

Fig. 4.   Sprouts on the seed tuber corresonds to the stems of the potato plant.

Main stems of potatoes grown from tubers are those that directly grow from the mother tuber. The sprouts (Fig. 4) on the seed tubers eventually grow into stems (Fig. 3). Stems that grow from the main stems are called lateral stems. The stem grows above ground but it has an underground section which is consist of the stolon, tuber, and roots. The length of this section of the stem is a function of planting depth and hilling-up. The greater the distance between the mother tuber and the top of the soil the more internodes will there be

The stems are generally green but the buried section is white (Fig. 2 and Fig. 3). Depending on species the stems could also be purple or reddish brown. 

Stolons are underground lateral stems (branches). They are easily identified as being thick white long structures arising from the nodes that are covered with soil (Fig. 5). Under favorable conditions, the apical end of the stolon eventually swells and develops into a storage organ called tuber. This stage is technically known as tuber initiation (Fig. 5). When the apical end of the stolon is exposed to light, it starts to produce chlorophyll and functions as a normal lateral stem or branch (Fig. 3).  One stolon potentially produces one tuber - hence the number of stolons in one plant determines the number of tubers produced.  

Fig.  5   Tuber initiation - apical ends of stolons developing into tubers.

Nodes are the points on the stem where buds, lateral branches, and  leaves originate.  In the case of the underground part of the potato, it is the point where the roots and stolons arise.   The space between nodes on the stem is called internode.  Planting deep enough to allow more nodes below the soil surface helps increase root and stolon formation.

Roots.   Potatoes that are grown asexually (from tubers) develop adventitious roots.  The potato plant has a root system that seem unsubstantial (Fig. 2) and growing superficially during its early growth stage [1].   Maintenance and conservation of soil moisture is important for this crop.   For small gardens, mulching is a practical management practice to take into consideration.    

Understanding the growth habits of plants help gardeners choose appropriate management practices for their crops.

Starting Life All over Again

 Fig. 1  A new plant from a leaf cutting.  African Violet (Saintpualia spp.)

Regeneration is the natural process by which some plants or plant-parts replace and restore separated parts to resume a complete plant again. When this phenomenon is applied for the purpose of multiplying the number of plants without the use of seeds, the process is called cloning or vegetative propagation.  The resulting new plant is called a clone.   A clone is a regenerated plant (Fig. 1).  A plant part - such as root, stem, or leaf, can be manipulated into forming new plants by severing it from the mother-plant.  

Most gardeners must have seen or grown an African Violet as a houseplant.  African violet is a good example of a plant that can be cloned easily. To own one plant means that you have a mother-plant that can give you many new plants.  

Fig. 2   Leaves harvested from a mother-plant.

The following pictures demonstrate some of the events that happen during the process of regeneration.  

Fig. 3   Callus formation and Root Differentiation

Callus Formation.  Plant parts such as leaves, when forcibly detached from the mother plant, undergo stress.  The natural response for such plant parts (just like in other life forms) is to start healing.   The first step in the healing process is the formation of soft protective tissue, known as callus, to cover the cut or wound.  Callus is characterized by a thickened outer tissue which is brought about by the rapid formation of undifferentiated mass of cells.  In Fig. 3, the brown colored end of the petioles is the callus.

Fig. 4    The roots are identified from the callus by shape, direction of growth and color. 

Root Differentiation.  The initial purpose of the callus is to form a protective surface over the wound to prevent further damage to the leaf.   As long as the conditions are favorable, cells continue to grow even after the wound has healed.   The leaf that was once a part of a plant will now start its own.  Cells begin to respond to chemical, hormonal, and physical factors which trigger differentiation.   Differentiation is the process wherein new cells take on new and identifiable form and role.  When the wound that triggered callus formation is  completely healed new events begin to happen.   Instead of continuing to grow and clump with the callus, new cells begin to be different.  Fig. 3 and Fig. 4 show roots forming from the callus.  The first sign of new life from the leaf has begun.  However, an old leaf with roots does not make a plant.  Something still has to happen.

Fig.  5   Shoot differentiation above the roots.  

Shoot differentiation.   Cells continue to multiply as shown by the increased root mass (Fig. 5).  The leaf (that was detached from a mother-plant) advances further to regenerate into a complete functioning plant.  The wound and the area around it is now the center of various physiological activities.  Not only have cells differentiated into roots but some begin to differentiate into shoot around the girth of the petiole just above the roots (Fig.5).  The shoots which are the part of the plant that will eventually bear the leaves and flowers have emerged.  

Fig. 6.  Trichome-covered  shoots emerging around the girth of the petiole.  

Note that differentiated tissues immediately assume the appearance of the organ.  The shoot buds contrast with the roots by the following characteristics:  presence of trichomes; green coloring which indicates the presence of chlorophyll; the form; and location and direction of growth (Fig. 6).   Cells that differentiate into roots tend to grow towards the ground and those that differentiate into shoots grow upwards.   Differentiation can be paralleled to the sorting of citizens into their political inclinations - some will be Republicans while others will be Democrats.  Regardless of the direction and position of growth, all plant parts play a key role in the overall functioning of the plant. 

Fig. 7    Root hairs growing from the initial roots.

Steps in Cloning African Violets through Leaf Cuttings1.  Take leaves from the outer ring of the foliage.  Make sure to include part the petiole.  Leaf blades can be used - new plants grow from the midrib, however, the petiole, when cut diagonally, provides a greater surface are for more shoots to grow.
2.  Fill up a pots with sand, perlite or potting soil.  Potting soil and recycled plastic containers can also be used as seen in Fig. 2.  Water until just moist and not soggy.
3.  Lay the leaves with the cut surface touching the media  (Fig. 2).  Cover the pot to prevent fast water loss.
4.  Maintain soil moisture.
5.  Wait and observe till plants develop and ready to be transplanted. 

Fig. 8    New plants - clones of the mother plant

Plants are super-organisms.  Given the right environment most plant tissues can regenerate into new plants.  

Parthenocarpy

Parthenocarpic Orange

Par.theno.carpy
Origin: Greek word parthénos = maiden; karpos = fruit)
Literal meaning: virgin fruit
Botanical meaning: enlargement of the ovary into a fruit without fertilization. 
(Parallel meaning: pregnancy without a developing-baby in the womb.)

Parthenocarpy is the phenomenon behind most seedless fruits.  Parthenocarpy is fruiting without the union of a male and a female egg cell.  The lack of fertilization means that there are no seeds in the fruit.  If there are seeds, they are not viable and are not capable of germinating.

Many times we take seedless fruits for granted and even despise the ones with seeds.  Although it is a natural occurrence in some varieties of some plant species (such as banana, persimmon, pineapple, and orange) parthenocarpy is an "abnormal" condition.   I say this because technically fruits are supposed to have seeds.  Seed is the reason for the fruit.  

Seedless grapes with traces of undeveloped seeds.

Fruit development begins with pollination. The moment the right pollen grain touches the stigma (the sticky surface of the pistil), fireworks of events happen as if a switch button has just been set to ON.  First a pollen tube develops as a passage way for the sperm nuclei in the pollen to the reach the ovules (part of the flower that develops into a seed). As soon as the pollen reaches its destination fertilization occurs and a zygote (fertilized egg = seed) is developed. Then several hormonal changes happen to signal a succession of events that support a continued development of the zygote. Gibberellin level suddenly rises resulting in the enlargement of the tissue surrounding the ovary. This tissue eventually differentiates to form the fruit.  Fruits tissues come in different charactreristics:  fleshy (as in grapes, peaches and apples), hard (as in nuts) or dry (as in dandelions and grains).  In short, fruit development occurs when a seed starts to develop. 

How does parthenocarpy happen? 

1.  Uncompleted Seed (Aborted Embryo).  Pollination triggers fruit development but in some cases the embryo is aborted before successfully developing into a seed.   The landing of pollen on the stigma is enough to trigger fruit formation that continues regardless of failed seed development.  Seedlessness through parthenocarpy does not involve fertilization.  However, seedlessness can still happen even after fertilization has already occurred through stenospermocarpy.  In this mechanism, the embryo is aborted just the same but at a much later time (1). The 'Thompson' and 'Flame' seedless grapes are examples of stenospermocarpy; traces of undeveloped seeds are visible when the berries are opened (see picture above).

2.  Genetic Disorder (Chromosome Imbalance).  Plant species which are triploids cannot successfully produce seeds - they are genetically sterile. The banana we buy from the grocery store is parthenocarpic because it is a sterile triploid (two sets of chromosomes from one parent and one set from the other) instead of the normal diploid where you get one set of chromosomes from each parent.  Pollination happens but fertilization does not.  The tiny black dots inside the banana are traces of the unfertilized ovules.  In the case of seedless watermelon, triploidy is induced through genetic manipulation. 

3.  Absence of a Perfect Mate (Self-Incompatibility).  Some plants species are self-incompatible - they are self sterile when pollinated by the same variety of plant.  In order to fruit, these species require pollens from a plant of different genetic makeup.  Navel oranges, pineapples, and clementines are examples of self -incompatible plants.  For example, when an orchard of the same variety of oranges is grown, fruits would come out seedless (parthenocarpic).    

4.  Manipulation by Steroids (Application of Growth-Regulators).  There are several growth hormones that play a role in parthenocarpy but for the current topic, our focus will be gibberellin.  Gibberellin is a phytohormone (plant produced-hormone) that is also produced by certain fungus called Gibberella fujikuroi.  Through this fungus, gibberellin-like compounds known as gibberellic acid (GA) can be produced apart from the plant.  GA is known to promote cell division and enlargement; when applied to plant at a strategic time and rate, the plant will respond accordingly.  This knowledge regarding the response of plants to applied GA and the knowledge that endogenous (produced within) gibberellin levels in plants increase upon fertilization and thus triggering fruit development have changed the horticulture industry.  Flowers can now be fooled into thinking that fertilization has taken place and thereby developing fruit-tissues.  In other words, fruits can be induced with the application of gibberellic acid.

Parthenocarpy is a delightful abnormality because the seedless fruit maintains the appearance and taste of its normal counterpart.  This is the reason why growers have capitalized on it to improve the commercial value of some crops.  Research work continues to exploit the application of parthenocarpy on more plant species where the seed is not for consumption.  

____________________
1) Table Grape Berry Growth and Development: A Review

Nocturnal Flower: Lagenaria siceraria

Lagenaria siceraria with nocturnal flowers.

Problem.  As I have mentioned earlier, I planted a variety of bottle gourd in my yard last spring and have successfully raised it to reproductive phase.  Hooray!  Several flowers - both staminate and pistillate have been forming daily starting from an early stage.   However, only one fruit per plant has developed and matured so far.  Back in the olden days in my grandfather's garden, I remember seeing several of green gourds of various sizes hang on trellises.  Using small twig, I used to write my name or draw hearts on the gourds that I can reach.   What's wrong with my plants?  How come fruit setting is so poor with my own plants?   I have made observations that might explain the sparse fruiting in spite of the flowers.

Explanation. The Lagenaria siceraria bears flowers that open at night.   They start to open at about 6:00 pm and remain open till the next morning - when they get spent under the scorching sun. Consequently, pollination happens at night also.   The plant depends on a nocturnal insect to pollinate its flowers.  Hawk moth has been reported to pollinate gourds.  Although I have not made the observation myself, this idea makes sense as most species of moths are nocturnal (they are active at night).   But there's one problem - with our dry climate, there is a lower population of these night-time pollinators in the area.   My theory is that the problem is due to limited night-time pollinators. 

Solution.  When planting Lagenaria siceraria in the future I will also include planting more plants that open at night to attract night-time pollinators in my garden.   If my theory is right, then increased attractants should result in more fruits. 

 

Developed fruit

White Flowers attracts nocturnal pollinators.

Well developed Fruit:  Two feet + long

Developing fruit

Opened Flower - Picture taken at 8:00 pm

Open Staminate Flower:  Picture taken in the morning

 Staminate Flower

The Lagenaria siceraria  produces well in a tropical environment but not in the semi-arid conditions of my garden.  Sometimes we transfer an organism from one to another location and expect that it would behave similarly.   Unless we can simulate the conditions of the old place then we are just dreaming.  

Some Things About Potatoes

Harvesting volunteer potatoes.

Volunteer plants are those that grow in the garden even in the absence of intentional care.  Volunteers arise from plants whose seeds and vegetative parts (such as rhizomes, tubers, roots and stems) survive under neglect.  This is natures' way of maintaining vegetation on this planet.  But when gardeners were born and their designs were printed, some of these volunteers have been labeled as weeds. 

In my garden potatoes would grow voluntarily every year even if I only planted once.   These are the potatoes that skipped my trowel during the previous harvest.   Early in the spring they would sprout right where they were left.   After three to four months when the leaves begin to turn yellow, we are ready to unearth the goodness that lies underneath the soil.   Today I will use these volunteer potatoes to share some useful lessons in gardening that I learned over the years.  Did I mention that I once was a potato scientist working with the International Potato Center in my younger days?  

Potato (Solanum tuberosum):  Tubers were very close to the soil surface.

A tuber hangs among many roots.

Tuber.  The part of the potato that we eat is called a tuber. It is a modified stem...not a root.    That's right the potato is technically a stem.   Tubers grow from a stolon which is a stem that grows underground.   This can be easily distinguished from the roots by their size and color.  Stolons are white and are much thicker than the roots. 

Tuber - "Bigger than my hand!"

Eyes.  The indentations on the potato tubers are called eyes.  Although they cannot see, believe me these eyes have brows. :)  Observe them the next time you peel some potatoes.   The eyes are the nodes of the modified stem.  On a regular stem, this is where branches would come out.  That is why when you keep your potatoes in your pantry for a long time, sprouts would come out.  If you plant those sprouting potatoes, those sprouts become the plants.  Did you know that potato varieties with deeper eyes are less desirable than their shallow-eyed counterparts?

Tubers harvested from one potato plant.

Greening.  Notice that the potatoes although harvested from the same plant did not have the same colors.  Some of them are green.  Greening in potatoes is the development of chlorophyll on the tubers caused by the exposure of the tubers to light.  The absence of hilling-up (raising the soil around the base of the plant) on these potatoes resulted in tubers that grow very close to the soil surface and thus exposure to sunlight. 

To prevent greening - always store your food potatoes in a dark place or cover them with a towel.  I don't recommend eating potatoes that show signs of greening for these reasons:  they don't taste good; they don't cook easily; and most of all they contain some amounts of toxic substances (glycoalkaloids).  

                              

Ugly potatoes with enlarged lenticels

Lenticels.  These are small openings on plant tissues that allow gas exchange.  In other words, they likened to the nostrils.  The bumps seen in the picture above are not diseases; they lenticels that have been enlarged.  The volunteer potato that we harvested was growing next to a leak in the drip line which created an anaerobic (absence of air) condition within the soil.  The lenticels had to open, as flared nostrils, in search of oxygen.  This is what happens when plants are over-watered - the lenticels swell and they can be a convenient entrance for microorganisms. 

I have to stop here but expect for more posts on potato-related topics in the future. 

The Imperfect Cucurbita Flowers

Unopened pistillate (female) flower.

There have been some zucchini flowers in my garden but no fruit has set so far.  When a baby zucchini appears, it is not a guarantee that a fruit will develop from it.  Sometimes this is a disappointing phenomenon especially to new gardeners. 

Staminate (male) flower.

Cucurbits have imperfect flowers.  Flowers are either perfect or imperfect.  Perfect flowers are those that include both pistil and stamen.  Imperfect flowers on the other hand, are those include either a stamen (staminate or male flower) or pistil  (pistillate or female flower) but not both.  Zucchini, just like all other cucurbita plants, bears imperfect flowers. 

Then there are two kinds of plants with imperfect flowers:

1.  Dioecious plants are those that have either male or female flowers.  In this case there need to be two plants of different sexes for pollination to happen.  Examples of this type are holly (Ilex spp.), willow (Salix spp.) and poplar. 

2.  Monoecious plants are those that carry the same sexes (pistillate and staminate flowers) in one individual plant.  Good examples of this type of plant are corn, and cucurbits (cucumber, pumpkin, squash, and gourds, etc). 

Cucurbits are monoecious plants.  They bear both pistillate (female) and staminate (male) flowers on the same plant.  Pistillate flowers are those that have a miniature squash at the base although at this point it is still an unfertilized ovary.  The squash will develop only when the pistillate flower is fertilized or pollinated.  

With the exception of the hybrid squash, cucurbita plants normally send out staminate flowers first.  When the plants are well developed they will be able to support multiple flowers - male and female flowers opening at overlapping intervals allowing pollination to take place.  Although the earlier flowers do not end up becoming fruits they are useful because they are like banners of invitation to the bees.  The colorful flowers invite the busy pollinators to come and stay around. 

Zucchini: An example of a cucurbita plant.

Understanding the growth habits of plants helps us explain some of our successes and failures in growing them.