370 



STRUCTURE AND LIFE HISTORIES 



The sterile branches produce smaller side branches at 

 the nodes. Chlorophyll is formed in the cells of the cortex, 

 and stomata in the epidermis permit the exchange of 



FIG. 267. Equisetum arvense. P, sterile branch; P l , fertile branch 

 with strobilus, or cone; R, rhizome (underground); T, cross-section of 

 cone, showing insertion of sporophylls in a whorl; N, N l , sporophylls 

 with pendant sporangia; S, S l , S z , spores with coiled elaters (el). 



gases necessary in photosynthesis and respiration. The 

 sterile branches elaborate practically all of the food neces- 

 sary to nourish the underground stem and the developing 



