CHAPTER XI 



WONDERS OF THE LEAF 



Its Function in Plant Growth and Its Important Relations to Humanity 



and All Other Forms of Life 



/ think that I shall never see 

 A poem lovely as a tree. 

 A tree whose hungry mouth is prest 

 Against the earth's sweet flowing breast; 

 A tree that looks at God all day 

 And lifts her leafy arms to pray; 

 A tree that may in summer wear 

 A nest of robins in her hair; 

 Upon whose bosom snow has lain; 

 Who intimately lives with rain. 

 Poems are made by fools like me 

 But only God can make a tree. 



— Joyce Kilmer. 



The leaf of a tree, shrub or plant is such a 

 common feature in Nature's productions that 

 it is an object universally recognized on sight, 

 but acquaintance with its origin, growth, its 

 function in plant life, its marvelous mechanism 

 and its relation to all animal life are per- 

 haps matters not so commonly understood. 

 We have constantly under our vision so many 

 leaves, green and fresh in the spring and 

 summer, and dead and dessicated in the fall 

 and winter, that the most of us appreciate 

 them only for the beauty they give to Nature 

 and the comfort they may afford us in the 

 former seasons, and regard them as a nui- 

 sance, if we think of them at all, in the lat- 

 ter. Another condition probably contributing 

 to the lack of general knowledge of the leaf 

 is the absence of the spur of necessity. In a 

 country like ours where the soil is as pro- 

 ductive and climatic conditions so favorable 

 to plant life, insuring annual recurrence of 

 abundant crops, we have little occasion to 

 think of, worry about, or inquire into the 

 source of our food supply, quantity or qual- 

 ity. The only anxieties we have in the mat- 

 ter are confined to the exertions and ex- 

 penditures necessary to acquiring the quantity 

 we must have to sustain our existence or 

 appease our appetites. 



However, in such parts of the globe sub- 

 jected to droughts causing total failures . of 

 crops with ensuing famine, the unfortunate 

 people inhabiting the districts have an object 

 lesson, most severe and destructive in its 

 operation, showing how all life belonging to 

 the animal kingdom is wholly dependent 

 upon productions of the vegetable kingdom 

 for the maintenance of existence. 



In the bodies of all animal life, including 

 mankind, there is a continual wastage going 

 on in the life cells, which must be renewed 

 by taking into the system those certain 

 chemical elements existing in what we know 

 •» as food, required to repair the waste, or 



sooner or later death occurs by what we call 

 starvation. The peculiar as well as im- 

 portant fact in this matter is that animal life 

 cannot assimilate the necessary chemical ele- 

 ments, chiefly oxygen, nitrogen, hydrogen 

 and carbon, in a form acceptable to the re- 

 quirements of the life cells without the aid 

 of the vegetable kingdom. 



Protoplasm with which the life cells are 

 filled is composed of the chemical elements 

 just enumerated, and is the physical basis of 

 all life of both kingdoms. Members of the 

 animal kingdom being unable to elaborate 

 protoplasm direct from the elements, Nature 

 has provided that the vegetable kingdom 

 shall assemble them with others that may be 

 required, and manufacture them into com- 

 pounds varying in character and form. These 

 are recognizable in succulent plants, grain, 

 seeds, fruits, etc. Another peculiar feature 

 is that the vegetable kingdom members can- 

 not work up these "compounds" from the ele- 

 ments direct, but must find them in the air, 

 the water and the soil in gaseous and soluble 

 combinations. For example, the carbon is 

 derived from carbonic acid gas that forms 

 a slight portion of the atmosphere in which 

 we live. This gas, which is a combination of 

 carbon and oxygen, is taken into the plant 

 principally through the leaves. The nitro- 

 gen is taken principally from the earth, but 

 also from the air, where it is always mixed 

 with oxygen, as it is also in the soils with 

 the addition of other elements in the form 

 of nitrates that are soluble, for the roots of 

 the plant cannot assimilate or take up solids. 

 The hydrogen is also in combination with 

 oxygen forming water. The plants after tak- 

 ing these up, use as much of them as are 

 necessary for the increase of their protoplasmic 

 cells. The surplus furnishes the material for 

 cell walls and substances such as seeds, pro- 

 viding for the reproduction of their kind, and 

 bulbs, rootstocks, cotyledons or seed coats for 

 the nourishment of the young plants at the 

 outset of their existence, also for the resin, 

 turpentine, sugar, tannin, etc., so useful to 

 the human family. The unused excess con- 

 sisting largely of oxygen and some carbonic 

 acid is returned to the air. 



When we consider that these fruits, grains, 

 bulbs, etc., are produced by plant life in such 

 enormous quantities, away beyond what is 

 necessary for reproduction of its kind to- 

 gether with the fact that all animal life 

 would perish for the lack of food supply with- 

 out this surplus, do we not distinctly see in 



