STEMS AND THEIR MODIFICATIONS. 51 
part is its food storage? Are its roots fibrous or 
storage, and what is their origin? 
B. Life Problems. 
1. 
9 
ale 
3. 
What is the purpose of plant stems? 
Do all stems assume the same direction in growth? 
Why? 
Where does the linear growth occur? 
Experiment 20. 
Where and how do stems increase in the transverse 
diameter ? 
Where are the upward and downward paths of the 
sap? 
Experiment 11. 
What is the destiny of winter buds? 
What is the purpose of branching? 
What is the purpose of various stem modifications ? 
Explain the presence and hardness of knots in 
lumber. 
What is the purpose of pruning ? 
. Explain pollarding of various trees. 
Of what advantage is it to grass stems in being 
hollow ? 
Explain plant propagation by stems. 
What are the economic products of stems ? 
How do gravity and light affect the growth of 
stems ? 
Experiments ai and 22. 
How do annual, biennial, and perennial stems differ? 
