Plant Dermal Tissue – Stomata, Root Hairs and Trichomes

Plants like all complex life on earth are organisms, made up of organs.  Leaves, stems, roots and flowers and fruits are organs found in plant which are made up of tissues.  Tissues are just made up of a combination of cells working together.  The tissue types found in plants are ground tissue, dermal tissue and vascular tissue.    Ground tissue is where cells that do the basic plant metabolism are found. Vascular tissue is where cells form tubes to transport material around the plant, much like our veins, arteries and capillaries.  The dermal tissue is the outer layer of the plant.  Most plants have a waxy layer called a cuticle that protects the plant from UV damage, prevents dehydration and can help protect from predation.  Under the cuticle, in the epidermis we find some specialized cells.  Guard cells are specialized cells found in pairs.  The opening between the guard cells is called a stoma (stomata is plural).  The stomata are where plants take in CO2, and release H2O generated during photosynthesis.  Many plants have a lot of stomata under the leaf, and indoors without rain, you may find increased plant growth if you mist or apply foliar spray to the leaves to rinse the dust out of the stomata.  However, mold can also benefit from foliar sprays, if you are only growing plants indoors under a light, and they only live a few months, you might not need to clean out the stomata, but if you have plants indoors that are year’s old, maybe spring cleaning should include a shower for your plants.

Other outgrowths of the dermal tissue are trichomes and root hairs.  Root hairs occur below ground, and are very important to plants because the root hairs increase the surface area of the roots, increasing water and nutrient uptake.  Many beneficial bacteria and mycorrhiza fungi are actually smaller than root hairs, so they increase nutrient and water uptake.  Your roots should be white and‘fuzzy’ if your plants are healthy, the fuzzyness is the root hairs seeking water and nutrients for your plant. Root hairs usually only last for 2 to 3 weeks and then die off.  This means you will find healthy root hairs at the ends of your roots, which makes sense, since the plant may have used up nutrients around the old root hairs.  The take away message   is that you want to minimize damage when potting up, which is one reason I recommend using the starter plugs vs. just plain sol for seedlings.
Trichomes are a general term for outgrowths that occur on the stem and/or leaves.  I could write many posts about the different kinds of trichomes.   In many plants these little ‘hairs’ help plants regulate water and heat loss.  They can also help with predation with both small and even large herbivores.  In some plants substances are secretedseveral basic functions or advantages of having surface hairs can be listed.  Studies of trichomes on plants subjected to frost show the ‘hairs’ keep the frost away from the living surface cells.   Other studies show that dense coatings of “hairs” reflect solar radiation, protecting the more delicate tissues underneath
Good Growing,
 Dr. E.R. Myers


How to Get Cloning Success for 20 Generations and Counting…

Do you know about the first mammal ever cloned?  The sheep they names Dolly.  Dolly was just one of many attempts to clone a sheep, she was the first that survived.  It was heralded as great success.  However, many people do not know the end of the story,  Dolly had to be euthanized when she was only 6 (sheep live to 10-12 commonly)  The problem was she was suffering from geriatric diseases.  The problem with cloning is that cells keep track of your age, so if you clone a 5 year old sheep, its cells will know, and act, like they are 5 years old the day it is born.  This limits animal cloning today, since you need to wait for an animal to mature to know if it has the characteristics you want in the clones.  The same is true for plants, the cells know how old they are.

Good growers know that you can only clone a plant so many times.  Many scientific publications have shown as few as 5 times are possible to get a plant to clone without changes in growth, yield etc.   I have a friend that has cloned her plants over 20 times, and has no noticeable difference.   Here is the trick...  Plants measure days in light and dark cycle, with a substance called phytochrome, (click here to read a post about phytochrome and plant flowering)  so it would make sense that a plant that was kept on 24 hours of light might think it was one day old.  This would make a HUGE difference in cloning longevity compared to growers that use an 18/6 light cycle.   A plant on 18/6 will be a month or more old when you clone it, (it will have had 30 days and 30 nights) and if its offspring are cloned using 18/6 they will add another month to the age.  After a few generations of cloning, the plants will think it is a year old, which for annuals means they will start to show growth abnormalities and have reduced yield etc.  Compare this with a plant that was on 24/7 for a month, it might think it is only a single day old!  If the next generation are then put on a 24/0 light and then cloned, the plants would be two days old.  This could be a way to have cloning work for maybe 100’s of generations. My friend is at 20 and counting with no signs of problems.  If any readers have any input, on this topic, please let me know.
Good Growing,
Dr. E.R. Myers

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Plant Knowledge to Make You a Better Grower – Plant Growth

Good growers are observant, and learn everything they can about the plants they grow.  There is an incredible amount of plant diversity, and as more and more people grow indoors and out, the types and varieties of plants that people will grow will increase.  There are certain aspects of plants that are the same for all plants.  Larger plants are usually termed vascular plants, because like us, they have veins that move water, nutrients and waste products around the plant.  Mosses are examples of plants that do not have veins.  The lack of veins means that non-vascular plants are limited in size because water has to diffuse through the plant to get to all the living cells.

Vascular plants only grow in certain areas called meristems.   The meristems are areas where cells divide, one cell splits into two cells, one of the cells can become specialized into a root, stem, leaf, or vein tissue, the other can be divide again forming another specialized cell.  Meristem cells act like stem cells in animals. 

Primary growth is how plants get taller.  This occurs in the apical meristem.  The apical meristem for most plants is at the top of the plant, so most plants grow from the top.  Plants do not grow like you and me, if we grew like plants, we'd only grow from the head up.  An exception to this is grass.  Grasses are one of the most widespread plants, found on 6 continents because they grow from the bottom.  This means that grazing and mowing do not damage the apical meristem, and the grass can grow back.  How well would a rose or oak tree do if you mowed it each week like a yard?  ** Here is the take away message** Since the tops of your plants are where new growth will occur, make sure you do not burn the tops of your plants with lights.  This is one of the most important areas of the plant so you want to protect it.  To do this you want to take the temperature of your plants at the tops.  It is in the tops of your plants where most of the metabolic activity is taking place, so you want the temperature and humidity to be optimal at the tops.  I use a thermometer with a separate cord and I put it at the top of the grow area, where it is usually hottest, and I hang the secondary cord down and lay it on the stem at the top of my plants so I know what the temperature is at the plant tops.  Most plants do well with temperatures in the low 80’s, and some people say upper 70’s gives even better growth.  You can figure that out for yourself with your plants in your grow area.

Woody plants get thicker by secondary growth.  Secondary growth or thickness occurs in lateral meristems.  This is a tube like area on the stems were cells divide outward increasing the girth of the plant.  I will be talking about plant organs in future posts, leaves, stems, roots and flowers/fruits.  Until then….

Good Growing,
Dr. E.R. Myers