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 1 , 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 2 , 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 
