—J. E. Carpenter
The growth and development of a plant, though such a common thing, is full of very real wonder and mystery. It takes only a little observation to discover the various stages in the process, but how they are brought about and by what laws they are governed, not even the most astute investigators can always say.
To the lay mind, the statement that the plants depend upon the soil for their nourishment is quite self-evident, yet it is extremely inaccurate. It is now quite certain that the vegetable world relies upon the air for its largest and most important food supply. The great mass of carbon which is the chief constituent of all plant structure is drawn almost exclusively from the atmosphere. While it is true that many vital elements are obtained from the earth, all green plants manufacture the greater part of their solid material out of the carbon dioxide of the air. Of what the plants do obtain from the soil, water makes up the largest bulk. The bread and meat of the plant world is carbon dioxide; the drink is soil water in which is dissolved certain essential salts and condiments.
A chemical analysis of a Green Pea will show approximately 46.5% of carbon, 4.2% of nitrogen and 3.1% of all other elements, exclusive of the hydrogen and oxygen which make up the water permeating all tissue.
This is truly a startling fact. Instead of belonging to the earth, the plants then belong primarily to the air. The air is their natural habitat; the earth serves to give them a fixed place in the world and provide them with flavoured water to drink.
Plants are born from seeds, the joint product of two previous individuals; they live by eating and drinking; they marry and in turn rear families of their own. It is our purpose in this chapter to show, in a very definite way, that this is not mere figurative language but a common-sense statement of fact.
The cycle of plant life can be illustrated by any dicotyledonous, herbaceous annual. If one is so inclined he may hark back to his high school days and plant a few Beans in a box as a practical illustration of the facts stated here.
The first action of the planted Bean is to absorb water to a prodigious amount, and so wake the quiescent life forces which may have been slumbering within it for years. It is a law of animal and vegetable life that all vital processes must be performed in solution. Without water, life is dead or somnolent.
When Nature made the Bean, she left a small opening or window in its skin-wall called the micropyle. Through this opening of the water-swollen seed, now issue two pale sprouts. One is long and pointed; it is the radicle or incipient root. The other is stubbier and is tipped by a cluster of folded, yellow-green leaves; it is the plumule or incipient stem. With unerring exactness, the radicle grows down into the soil and the plumule feels its way up into the air.
By this time, the seed has burst its walls and split into two halves, which indicates that it belongs to the dicotyledonous group of plants. As the seedling continues to grow, these cotyledons begin to shrink and shrivel. The plant is living on their substance until it can begin to make its own. In the case of the Bean, the stem lifts the emaciated cotyledons up into the air, where they act as leaves until the tiny green things at the stem’s tip have expanded into those important organs.