14 NEBRASKA STATE HORTICULTURAL SOCIETY. 



are favorable or not. Upon a fair-sized apple leaf, there are no less 



than from 350,000 to 400,000 

 of these pores, and in some 

 cases they run much above 

 these almost incredible figures. 

 In some plants, as cottonwoods, 

 sunflowers, cabbages, etc., they 

 occur on both sides of the leaf, 

 but in the apple they are con- 

 fined to the under side. A tree 

 is thus a thing with a myriad 

 of mouths, through which it 



breathes in the carbon dioxide 

 FIG. 1. A small portion of the lower skin of 



an apple leaf, showing the breathing pores, as one OI the most important 

 magnified 725 times. o f its foodg> It also takes in 



through its leaf-mouths another gas, some of which eventually becomes 

 a part of the plant body, and hence it must be called a food matter. 

 This gas is oxygen, the same gas which we take into our lungs with 

 every breath we inhale. 



The carbon dioxide and a little of the water are broken up in the 

 green cells of the leaves, and from the resultant fragments starch is 

 made. The latter constitutes a more important secondary food of 

 plants, inasmuch as it contains almost exactly the same substances as 

 those which constitute the bulk of the solid part of the tree. Although 

 starch is made in the green leaves, it may find its way to all parts of 

 the tree, even to the remote roots away down under ground, and every- 

 where, sooner or later, it is used by the plant in the building up of 

 its substance. At the same time the other food substances taken in by 

 the roots are used by the different parts of the plant as needed. The 

 idea sometimes advanced that all food matters taken in by the roots 

 must go to the leaf in order to be " elaborated," is quite erroneous. 

 These substances are used whenever they are needed, whether in the 

 roots themselves, or in the twigs, or even the leaves of the tree top. 



There is one thing which must be discussed at this point, although 

 it is only indirectly connected with the question of the food of the 

 tree. I refer to the loss of water from the aerial parts of the tree, 

 and particularly irom the leaves. It can easily be shown that the 

 inside of a leaf is much more moist than the air which surrounds it; 



