58 



PLANT BIOLOGY 



horizontal branches are interesting in this connection. 46. Note 

 the enlargement at the base of a branch, and determine whether 

 this enlargement or bulge is larger on long, horizontal limbs than 

 on upright ones. Why does this bulge develop? Does it serve 

 as a brace to the limb, and is it developed as the result of constant 

 strain? 47. Strength of stems. The pupil should observe the 

 fact that a stem has wonderful strength. Compare the propor- 

 tionate height, diameter, and weight of a grass stem with those of 

 the slenderest tower or steeple. Which has the greater strength ? 

 Which the greater height? Which will withstand the most wind? 

 Note that the grass stem will regain its position even if its top is 

 bent to the ground. Note how plants are weighted down after a 

 heavy rain and how they recover themselves. 48. Split a corn- 

 stalk and observe how the joints are tied together and braced with 

 fibers. Are there similar fibers in stems of pigweed, cotton, sun- 

 flower, hollyhock ? 



Fig. 68. — Potato. What are roots, and what stems ? Has the plant more than 

 one kind of stem ? more than two kinds ? Explain. 



