104 Plant Life and Evolution 



earlier geological times. Unlike the ferns as these 

 plants are in their general habit, they nevertheless 

 show many points of resemblance to the lower ferns 

 in their characters, both of gametophyte and sporo- 

 phyte, and it is probable that there is a real, although 

 remote relationship existing between the horsetails 

 and ferns. 



In the Northern forests one often finds covering 

 the ground, evergreen trailing plants whose slender 

 creeping stems send up little branching shoots closely 

 set with small leaves, so that they suggest little 

 evergreen trees. These are " club-mosses " belong- 

 ing to the genus Lycopodium, and one of them, 

 popularly known as " ground-pine," is every year 

 sent in great quantities to the Northern markets at 

 Christmas time for making wreaths and festoons. 

 These club-mosses, or Lycopods, represent a third 

 class of pteridophytes, which differ so much from 

 the ferns and horsetails as to make it likely that 

 they are not at all related to them, but have orig- 

 inated quite independently (Fig. 13, A). 



A second genus, Selaginella, contains several hun- 

 dred species, a few of which occur in temperate 

 regions, but most of them are tropical. A num- 

 ber of species are common in greenhouses, where 

 their delicate moss-like foliage is very ornamental. 

 These cultivated species are often erroneously called 

 Lycopodium, but may be distinguished from the 

 true Lycopodiums by having two sorts of spores, 

 large and small. In the character of its spores, 



