This section is from the book "The Gardener's Monthly And Horticulturist V24", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
" D. P. F.," Hanover, York Co., Pa., asks : " Can you tell me where to find any information in regard to the evolution of heat in the growth of plants? Is there much heat evolved and is this in proportion to the amount of growth and vigor or not?"
[We do not think there has been much written anywhere about this subject, except what has appeared from time to time in the pages of our magazine.
We have taught in our pages that in all vital action, equally in the vegetable as in the animal kingdom, the evolution of heat is an attribute of life. In other words the decomposition of food is essential to life, and heat is evolved by this decomposition. That there is a specific degree of heat in plants is proved in various ways. For instance, if a maple tree be subject to several weeks temperature, say of near zero, and suddenly the temperature rises to 38°, the sap will run out in streams from a cut branch, and, during the night following icicles often form a foot long. If there were not a specific degree of heat in plants the juices of the tree would freeze solid, and it would take days to thaw when protected as it is by non-conducting bark. The sap could not run out freely, immediately the temperature of the atmosphere rose above the freezing point.
Again, a very good illustration of the way in which a plant can hold its heat in spite of external influences may be seen on a warm day towards spring, when the leaves and fences are covered by thawing snow. The steam will arise under the warm sun, from corn stalks, dead leaves, or dead wood in fences, but not from living leaves. The dead matter readily receives heat from the sun - the living plant resists heat as readily as it resists cold. A living tree seems cool to the hand in hot days, when a dead tree or a post is warm.
Sometimes we find parts of plants warmer at times than at others, and especially when they have a great deal of work to do - just as we find to be the case in animals. It has been found that when a palm or a large flowered aroid is about to open its blossoms a thermometer thrust into its spathe will show a temperature of 80°, while the external air may be but 70°. This shows that plants have some specific heat.
Just what this is, however, so far as we know, has never been determined. What has been ascertained is chiefly in the direction we have here outlined, and may be reduced to little more than this, that life in plants and life in animals in its relation to heat is substantially the same. - Ed. G. M].