HORSETAILS AND 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 Fic. 195.— Branch of Selaginellu bearing strobili. 
(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. 
