228 



BOTANY. 



424. The branches, when present, are in whorls. Both 

 the main axis and the branches are in most cases richly 

 supplied with chlorophyll -bearing tissue ; in some of the 

 species the stems which bear the spores are destitute of 

 chlorophyll. All the species have underground stems, 

 which bear roots and rudimentary sheaths, and which each 

 year send up the vegetating and spore-bearing stems. 



425. The Horsetails are 

 perennial plants. In some 

 species the underground por- 

 tions, only, persist, the aerial 

 stems dying at the end of 

 each year; these are called 

 the annual-stemmed species. 

 In other species the aerial 

 stems also persist; the latter 

 are hence known as peren- 

 nial-stemmed. 



Fio. 136. Fig. 137. 



FiQ. 136.— Part of a green stem of the Great Horsetail (Equlsetum tel- 

 mateia), showing its structure ; and a whorl of united leaves, with part of 

 a whorl of branches. Natural size. 



Fg. 137.—^, part of an old cone of the Great Horsetail, showing three 

 separated whorls of shield-shaped leaves ; B, three shield-shaped leaves, 

 slightly magnified ; st, stalk, and s, expanded part of leaf ; sg, the spore- 

 oases, 



