144 MORPHOLOGY 



quence of this abandonment of leaves as foliage, photosynthesis is 

 entirely a function of the green tissue of the stem. Many of the 

 older forms were leafy, but all Equisetales are characterized by the 



FIGS. 332-338. Equisetum arvense: 332, fertile branches from the dorsiventral 

 stem, each bearing a terminal strobilus, one of them mature; 333, sterile branch; 

 334, 335, two views of a sporangiophore (so-called " sporophyll ") > 336-3?^. spores, 

 showing the unwinding of the perinium. After WOSSIDLO. 



