stem Work 



surface of leaves where the food is most easily 

 reached ? 



The second function of the stem will be more 

 readily appreciated after we have briefly discussed 

 the functions of the leaves. All leaves are produced 

 in buds and in age-order, the younger nearer the 

 apex of the stem bearing it. The stem carries 

 them into the light, and the spaces at which the 

 leaves are set may be more or less lengthened as the 

 stem grows in order to effect this, or the stem may 

 twist between the leaves for the same purpose. 

 The arrangement of the leaves on the stem and their 

 disposal are both connected with the need for light. 



The special functions of the leaf are also two : 

 the making of food and the getting rid of water. 

 Both these functions, as we shall see, involve the 

 passage of gases into or out of the leaf, and this is 

 effected through the curious pores called stomata 

 which are found in the skin of the leaf, mostly on its 

 under side. These pores are surrounded by two 

 guard-ceUs, which open when the plant is fuUy 

 supplied with water or when it is exposed to Ught, 

 and which tend to close as the waiter supply or the 

 light fails, and may close completely. 



Food-making is a power which, of aU living things, 

 green plants alone possess. The raw materials for_ 

 it are water and earth-salts, which are obtained by 

 the roots, and carbonic-acid gas, which passes from 

 the air through the stomal openings into the leaves. 



11 



