156 



THE STEM PROPER 



300. — Section across a young twig of 

 box elder, showing the four stem regions : 

 If, epidermis, represented by the heavy 

 bounding line ; c, cortex ; w, vascular cylin- 

 der; p, pith. (From COULTER'S "Plant 

 Relations.") 



of dearth, to subsist for a while on the buds and bark 



of trees. 



221. Difference between 

 Dicotyledons and Monocoty- 

 ledons. — Cut cross and 

 vertical sections of your 

 specimen, and sketch them 

 as seen under the lens, 

 labeling the different parts 

 that have been examined. 

 Refer to Figures 300 and 

 301 if you have any diffi- 

 culty in distinguishing the 

 parts. Notice the little 

 pores or cavities that dot 



the woody part in the cross section ; where are they largest 



and most abundant ? How are the rings marked off from 



one another .■" These pores are sections of the ducts already 



alluded to (Sees. 214, 



215). They are very 



large in the grape vine, 



and a cutting two or 



three years old will show 



them distinctly. Exam- 

 ine cross and vertical 



sections of a twig that 



has stood in red ink 



from three to twelve 



hours and observe the 



course the fluid has 



taken. (The rapidity 



with which the liquid 



is absorbed varies with 



different stems and at 



different seasons. It is 



301. — Section across a twig of box elder 

 three years old, showing three annual growth 

 rings, in the vascular cylinder. The radiating 

 lines {m), which cross the vascular region (w) , 

 represent the pith rays, the principal ones ex- 

 tending from the pith to the cortex (c). (From 

 Coulter's " Plant Relations.") 



most rapid in spring and slower in winter. In grape, 

 plum, and peach it ascends quickly.) What should you 



