HORSETAILS AXD CLUB-MOSSES 



203 



as are the gametophytes (prothallia) of ferns and equi- 

 setums, are subterranean tuberous bodies with no chloro- 

 phyll, on which the antheridia and archegonia appear (Fig. 

 194). In some forms of Lycopodium the tuberous prothal- 

 lium develops an aerial portion that is green and bears the 

 sex-organs. This strange subterranean and saprophytic 

 prothallium is in marked contrast with the prothallia of 

 ferns in its habits and 

 appearance.* 



118. Selaginella.- 

 The Selaginella forms 

 are much more numer- 

 ous than the Lyco- 

 podium forms, being 

 especially abundant 

 in the tropics, and are 

 often called the little 

 club-mosses on ac- 

 count of their smaller 

 size and more delicate 

 texture. It is these 

 forms that are com- 

 mon in greenhouses 

 as decorative plants. 

 There are often no 

 strobili very distinct 

 from the leafy stem, 

 the solitary sporangia 

 occurring in the axils 

 of the upper leaves 

 (Fig. 195). 



The most important fact in connection with Selaginella 

 is that all the sporangia in a strobilus do not produce the 



* The gametophytes of Lycopodium are so rarely found that it is 

 not expected that they will be seen by the student. 



FIG. 195. Branch of Selaginella bearing strobili. 



