THE SELAGINELLACE^. 



N the time of Linnaeus the plants that are now 

 referred to the genus Selaginella were thought to 

 be true club-mosses, and such species as were 

 then known will be found in old botanical works 

 in the genus Lycopodiiiui. There is, however, 

 this important difference between them. In the 

 lycopodiums the spore-cases bear many spores all 

 of the same size and appearance, which produce 

 prothallia of one kind, while in Selaginella the lower 

 spore-cases in the fruit-spikes each bear about four large 

 spores called megaspores, while the spore-cases higher 

 up in the spike bear great numbers of smaller spores 

 called microspores. When the microspores germinate 

 they form very reduced prothallia bearing only anther- 

 idia, and are therefore called male prothallia; while the 

 megaspores produce larger prothallia 

 with only archegonia, and hence are 

 called female prothallia. Both sorts 

 of prothallia begin to develop before '^bm*^(\>*'"vi-<si, 

 the spores have left the sporangia, but ^^^^^^'^S'^ 

 even after the spores have fallen, the 

 prothallia, unlike those of most of the Megasp^TTi-./^^/- 



nella ri4pestris. (Much 

 enlarged.) 



ferns and fern allies, never leave 

 the spores. When the prothallium in 

 the megaspore has nearly attained its growth, the thick 



