PRINCIPAL GROUPS OF PLANTS. 



99 



erosporous and the gametophytes resemble those in Selaginella, the 

 sperms are multiciliate and coiled as in the Ferns. 



Distribution and Uses of Lycopodiales. A number of the 

 Lycopodiums are common on rocks, damp woods, sandy bogs, 

 and illustrations of several of these are shown in Fig. 66. Some 

 tropical species are used in medicine; the spores of Lycopodium 

 clavatum, on account of their fixed oil, are used as a dusting 

 powder, and for burning in the production of flash lights (see 

 Vol. II). The Selaginellas, of which there are several native 

 species, are commonly used for decorative purposes. Some species 



II 



FIG. 61. Longitudinal section of young embryo of a Selaginella before separation 

 from the prothallus: et, suspensor; w, root; f, foot; hi, cotyledons; hg, ligules or bud scales. 

 After Pfeffer. 



are, however, also used in medicine, and it is interesting to note 

 that the spores of one species (Selaginella selaginoides) are used 

 like those of Lycopodium. 



While the Pteridophytes do not form a very conspicuous por- 

 tion of the flora at the present time and yield but few products 

 of use to man, it may be pointed out that in former ages they 

 formed the dominant vegetation of the earth. Many of the 

 ancestral forms of this group attained the size of trees and made 

 up the forest vegetation during the Devonian and Carboniferous 

 Ages, the latter being sometimes spoken of as the age of Pterido- 

 phytes. It is also called the Coal Age from the fact that the coal 



