CLUB MOSSES 



425 



sporophylls) . Not all of the stem tips are fertile ; that is, 

 not all of them bear the little bean-shaped, yellowish 

 sporangia. 



Some of the club mosses do not have the strobilus 

 so clearly denned as it is in the 

 equisetums, but in others the spo- 

 rangia-bearing tips have their leaves 

 more closely set together than those 

 of the sterile tips, and the strobilus 

 is very distinct. It has a club- 

 shaped appearance ; hence the name 

 club mosses. (See Figure 218.) 



Selaginella. This is the name of 

 a group of club mosses. Some of 

 the Selaginellas are quite common 

 in greenhouses. Their general struc- 

 ture and habit of growth are like 

 that of the club mosses already 

 described, but they are more deli- 

 cate and graceful. They are smaller. 

 Their leaves are both smaller and 

 broader. They are not such hardy 

 plants as the coarser club mosses. 

 (See Figure 219.) 



In tracing the history of plants 

 the Selaginellas are very interesting 

 and important. They have the re- 

 markable habit of producing two 



kinds of spores. Heretofore we have found but one kind 

 of spore. This habit of producing two kinds of spores 

 would be of no great interest to us if it were a habit of 





This is a picture of one of 

 the simplest species of this 

 genus. In it the sporan- 

 gia are not restricted to 

 certain leaves, but a spo- 

 rangium is usually found in 

 the axil of each leaf. Near 

 the top may be noted some 

 sporangia which have not 

 yet discharged their spores. 



