52 



INTRODUCTION TO PLANT GEOGRAPHY 



[CIIAP. 



plant or, more often, on separate (male and female) individuals. 

 Fertilization is again by a motile spermatozoid which, when water 

 is present, swims to the passive and protected egg. The body 

 formed by this sexual fusion develops into the sporophyte which, 

 when mature, consists of an absorptive foot, a usually long stalk, 

 and a more or less complicated and characteristic capsule. Fig. 14 

 shows both the gametophyte and sporophyte of different types of 

 Mosses, for here again the two generations are unseparated, forming 

 one continuous plant body, the sporophyte being at first parasitic 

 on the gametophyte but later becoming at least partly self-supporting 

 through its possession of chlorophyll. 



The spores, formed in the capsule and liberated often by some 

 complicated mechanism that works only in dry air (which is more 

 beneficial than moist air for their further dispersal), are again the 

 main mode of multiplication. But instead of growing directly into 

 a typical new gametophyte as in the Liverworts, they develop in the 

 Mosses, on germination, into an extra stage known as a ' protonema '. 

 This is an independent, cellular plant containing chlorophyll and 

 manufacturing its own food. It is filamentous and branched in 

 most types but in some it is thalloid, like the gametophyte of many 

 Liverworts. On the protonema develop lateral buds which grow 



