320 



STRUCTURE OF EQUISETUM 



and take little or no part in photosynthesis. These scale leaves 

 are arranged with great regularity at the nodes of the stem, and 

 owing to their close association they grow together, forming a 



Fig. 232. A common horsetail, Eqttisetum arvense: a, the green branch- 

 ing plant that lives through the summer — /, scale leaves; r, rhizome or under- 

 ground stem with tuberous storage organs, b. early spring shoot that bears 

 a spike or strobilus of modified spore-bearing leaves, sp. This stem is of a 

 light brown color and withers after the spores are shed. — H. O. Hanson. 



papery sheath with teeth-like points about the stem (Fig. 232, /). 

 It is noteworthy that in allied fossil forms large chlorophyll- 

 bearing leaves occurred. 



The stems are of two kinds, subterranean rhizomes that branch 



