The Stems of Plants 



115 



together form the eyes of tubers. Tubers, like other fleshy un- 

 derground stems, accumulate surplus food and multiply the 

 plant. The potato tuber has become 

 one of the most important sources of 

 food for man. 



Summary. Stems vary greatly in 

 structure, size, and position. Each 

 type of stem has certain advantages 

 and gives the plant characteristic 

 habits of growth. Each of these stem 

 types also fits into certain environ- 

 ments better than into others ; con- 

 sequently there are great differences 

 to be observed in the kinds of plant 

 stems in different habitats and dif- 



ferent regions. 



Fig. 64. Amaryllis bulb. A bulb 

 is a fleshy underground bud made 

 up of a short stem covered with 

 several layers of thick scales in 

 which food is stored. 



PROBLEMS 



What advantage in resisting wind have tall, columnar tree trunks over equally 



tall smoke stacks or monuments ? What disadvantage ? 

 What are the best trees for street planting in your locality? What trees now 



planted there are objectionable ? Why ? 

 Compare a tree growing in an open field with one of the same species growing in 



the woods. Account for the differences in arrangement of branches and leaves. 

 Which will furnish the better lumber, a tree grown in the open, or one grown in 



the forest? Why? 

 W'hat commercial products are derived from each of the several types of stems 



described in this chapter? 



