400 A TEXTBOOK OF GENERAL BOTANY 
ORDER SELAGINELLALES 
Selaginella. This genus is the only representative of the order 
Selaginellales. The sporophyte is a small, fernlike plant with 
small, scalelike leaves (Fig. 447). Some of the species are cul- 
tivated for ornamental purposes. The sporangia are borne singly 
on the upper surface 
near the base of the 
sporophyls. In some 
species the sporophylLls 
are similar to ordinary 
leaves, but in most cases 
they are smaller and 
agoregated into termi- 
nal strobili (Fig. 447). 
The sporangia are of 
two kinds (Fig. 448), 
microsporangia and meg- 
asporangia, and the 
sporophylls which bear 
them are called, respec- 
tively, mcrosporophylls 
and megasporophylls. A 
microsporangium con- 
Fig. 448. Sporangia and spores of Selaginella tains numerous small 

Upper left, megasporophyll with megasporangium Spores, mecrospores, while 
containing four megaspores (x 15); upper right, each megasporangium 
microsporophyll (x 15); lower left, megaspor : 
Et thee aed sun contains 4 foumaml naam 
(x 75); lower right, microspore (x 75) 
' - Spores, megaspores. The 
microspores give rise to male prothalli, and the megaspores to 
female prothalli. The male prothallus develops within the spore 
wall and consists of a single prothallial cell and an antheridium 
(Hig. 449). The female prothallus also begins to develop within 
the spore wall. As the prothallus continues to develop, the 
spore wall is burst and the apex of the prothallus with the arche- 
gonia is exposed (Fig. 449). The egg is fertilized by a motile 
