522 



HUTCHINSON'S POPULAR BOTANY 



FIG 665. LIVERWORT (Marchantia 



polymorpha). 

 With antheridial receptacles. 



We now come to those Cryptogams 

 in which the structure is entirely cellular, 

 the first division of which is the 



BRYOPHYTA. 



Class I. Musci. Mosses. 

 II. Hepaticae. Liverworts and Scale Mosses. 



In these classes we find an alternation 

 of generations, as in the Pteridophyta, 

 but there is a difference to be explained. 

 Beginning with the spore, we find it to 

 consist of a central mass of protoplasm, 

 in which are chlorophyll-grains, etc., in- 

 vested by an inner coat or endospore, and an outer coat, or exospore. 

 On germinating, the endospore and its contents burst through the exospore 

 and develop into a hair-like body the protoneme. Side shoots from the 

 protoneme develop into chlorophyllous scales in the Liverworts, and into 

 leafy stems in the Mosses. These in turn bear sexual organs archegones 

 and antherids (figs. 665, 666). 



In the protoneme of the Mosses cell-division takes place in one direction 

 only transversely ; but as this may go on indefinitely, we have the fila- 

 mentous form. Some of the cells thus formed send out lateral shoots which 

 in turn divide transversely, so that the protoneme may be ultimately many- 

 branched. Distinct buds are also produced 

 which develop into wiry stems, which are 

 clothed with two, three, or four rows of 

 leaves. The protoneme and this leafy 

 plant produced by it must be considered 

 as together constituting the oophyte or 

 sexual generation. The leaves of Mosses 

 are never stalked, and with the exception 

 of a line down the centre (midrib), and in 

 most cases along the margins, consist of 

 a single layer of cells : stomates being 

 therefore unnecessary, the leaves have 

 none : but the stem is often liberally pro- 

 vided with stomates. The midrib is not 

 always continued to the tip of the leaf ; on 

 the other hand, in many species it extends 

 bej'ond the tip as a fine hair-like point of 

 variable length. Around the three-sided 

 apex of the stem the leaves are more 

 densely crowded, and these are more or 

 less modified. They constitute the peri- 



Fio. 666. LIVERWORT. 



With archegcnial receptacle, (a) Cup-shaped 

 receptacle containing gemma. 



