54 THE PLANT: A GENERAL EXTERNAL VIEW 



under surface of the leaf are many stomates. (The Greek 

 word stoma means mouth.} A stomate is an opening in 



the skin of a leaf. It is so small 

 that it requires a microscope to 

 see it; there may be thousands 

 of stomates on a single leaf. (See 

 Figure 8.) Gases pass in and 

 out through the stomates. The 

 upper angle between the base of 

 the petiole and the stem is the 

 axil. If there is no petiole, the 



FIG. 8. A little of the under , 



surface of the leaf of Coieus, u PP er an g le between the base of 

 very highly magnified. TWO the blade and the stem is the 



stomates appear. ft J s m the axils of leaves 



that buds regularly arise. Buds develop into branches, 

 either flower bearing or leaf bearing or both. 



Now you know very well that more light falls on the 

 leaves than on any other 

 part of the plant ; the leaves 

 seem to seek the light. (See 

 Figures 9 and 10.} So it 

 does not surprise you to 

 find that the leaf is the part 

 of the plant in which photo- 

 synthesis principally occurs. 

 Up to it, through the veins, 

 come those materials from 

 the soil which it uses in 

 this work. Into it, through 

 the stomates, come those 

 substances of the air which 



FIG. 9. A nasturtium with light corn- 

 are necessary. Down tO it, ing to it from above. 



