RELATIVES OF THE FERNS 49 



vation in greenhouses, and almost everyone 

 can secure and grow examples for study. The 

 Common Selaginella, which often invades every 

 pot in a fernery, must be familiar to many, 

 although it is quite likely that not a few 

 gardeners would be puzzled to explain to what 

 group the plant belongs. Altogether there are 

 three or four hundred species belonging to this 

 family. A very singular group of club mosses 

 is that which is typified by the Quillwort 

 {Isoetes lacustris). This plant is very common 

 in the northern lakes of these islands, and is 

 found established at the bottom of the pool, 

 where it roots in the mud. 



It is only within comparatively recent times 

 that the life story of the club mosses has been 

 understood to any extent. Even now there 

 are many points which are only partially 

 explained. In the case of the Lycopodium, it 

 is in the cone-shaped processes that the little 

 spore cases {sporangia) are produced. With a 

 magnifying glass these may be distinguished, 

 and they are seen to be kidney-shaped and 

 attached to the upper side of the leaf. The 

 sporangia open when their contents are ready 

 for dispersal, and at that time an enormous 



