STEMS 



51 



usually the principal green parts of plants. In them 

 food is made. Some stems, however, are also green, and 

 in them too food is made. Perhaps you have noticed how 

 very green some young stems are. Under the thin bark 

 there is sometimes a layer which is quite as green as the 

 leaves themselves. In this 

 green layer of stems photo- 

 synthesis occurs just as 

 it does in green leaves. 

 Thus we find that stems 

 sometimes do the ordinary 

 work of leaves. You re- 

 call that we found they 

 also sometimes do the or- 

 dinary work of roots. 



There are some green 

 plants which have no food- 

 making leaves at all, and 

 such plants perform all of 

 their photosynthesis in 

 the stems. Cactuses are 

 the best known plants of 

 this kind. Perhaps you 

 have seen them under cul- 

 tivation. They are com- 

 monly found in conservatories where they are cultivated 

 on account of their strange forms and on account of the 

 beautiful flowers which they produce at long intervals. 

 It is in deserts that cactuses are found growing wild in 

 greatest abundance. Their fleshy, water-containing bodies 

 permit them to live where other plants would perish. 

 (See Figure 6.) 



Fig. 6. — The giant cactus. These leafless 

 stems are green and contain a great deal 

 of water. 



