THE FLOWEEING PLANT-^STEMS 355 



Isolate the elements of the stem by using 

 Schulze's macerating mixture. Draw several of 

 each kind of element found. 



Examine transverse and longitudinal sections 



through the growing point or punotum vegetor 



tionis. Section the other stems, and compare 



Avith that of the horse-chestnut and with one 



another. Notice particularly the tracheides, 



which form the greater part of the xylem in the 



pine stem. Draw several. Study especially the 



stems of the Begonia and Tradescantia. 



Make drawings of all of the sections studied. "What 



structural resemblances can you trace between any of 



these stems and the rhizome of the fern ? 



PHYSIOLOGY 



a. Movements. 



1. Geotropism. — Sow some seeds, as mustard, flax, 

 peas, and beans, in the meshes of a coarse 

 sponge, and keep the latter well moistened un- 

 der a bell-jar, placed near a window, until the 

 seeds germinate and the young stems appear. 

 Notice particularly the direction of several of 

 the stems of each kind of plant. "With a fine 

 camel's-hair brush, dipped into India ink, paint 

 four lines at equal distances apart, dividing 

 each stem into quarters, and running from the 

 cotyledons down to the surface of the sponge. 

 Turn the sponge upside down, being careful to 

 keep the plants in the same position as regards 

 light. Examine the plants both morning and 

 afternoon for several days. Does the direction 

 of the stems change? In what way? How 

 soon can you detect, by the bending of the lines 



