278 ESSENTIALS OF BOTANY 



It therefore leads a half-parasitic life like such seed-plants 

 as the mistletoe. 



The life history of a moss is as follows : The spore on 

 germinating forms a network of protonema, often of con- 

 siderable extent. This protonema finally produces buds 

 (Fig. 199, pi), which grow into leafy moss-plants (gameto- 

 phytes). These bear the non-sexual sporophytes, and so 

 on in a series of alternating generations (see Sect. 349). 



Some mosses produce antheridia and archegonia in the 

 . same leaf-cluster, while others produce only one kind of 

 sex organ in a cluster. In case the sexes are separated 

 the male plants bear the antheridia at the summit within a 

 sort of basin-shaped rosette or circle of specialized leaves, 

 which are often colored (not green). The female plants 

 bear the archegonia„ at the tips of the branches, where they 

 are hidden by closely appressed leaves of the usual sort. 

 Fertilization of the egg in the archegonium takes place 

 when the sex organs are wet by rain or dew. The sperms 

 are washed into the opening of the archegonium and make 

 their way through the mucilage which fills its neck until 

 they reach the egg at the bottom of the cavity. 



358. Summary of the Mosses. — The mosses form a more 

 united group than the liverworts, differing less among 

 themselves in vegetative habit and in the details of their 

 reproduction. None of the mosses are thallus plants and 

 no whole order of mosses ig aquatic, though some genera 

 are so. Mosses are evidently far more successful plants 

 than liverworts, as is shown by the fact that they are so 

 numerous and so widely distributed. This is due in part 

 to their reproductive power and also in part to the capacity 

 of some of them to endure great extremes of heat and cold, 

 moisture and dryness. The mosses, like the liverworts, 



