286 



Science of Plant Life 



columnar plants with scale leaves and spore-bearing cones on 

 the ends of the upright branches. These are the remnants of 

 a group that made up a large part of the vegetation during 

 the carboniferous period. Many of the species are evergreen. 



The equisetums are for the 

 most part stream-margin and 

 swamp plants, and, as might be 

 expected, the stems have air 

 cavities extending throughout. 

 In some *species the stems de- 

 velop at each node whorls of 

 slender branches, which to- 

 gether form a brush, suggesting 

 the common name " horse-tail " 

 for the group. 



Like the ferns, most of the 

 species develop an extensive 

 system of underground stems 

 from which the upright branches 

 rise. In the absence of foliage 

 leaves, the stems do all the 

 photosynthetic work. The 

 roots are small, like those of 

 the ferns. Spores are pro- 

 duced in the cones which termi- 

 nate the upright stems. 



The club mosses. These 



Fig. 169. The common field cquisetum. ^rc Creeping and trailing ever- 

 Rootstock with sterile branches (B), green plants found in rich woods 



spore-bearing branches U) and tubers ^^^ ^ particularly in the 



(C) . D shows the spores with their ap- o > t j 



pendages. northern United States. They 



