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, pl), 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 léaves, 
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 is 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, 
