II MUSCINEM— HEPATIC^— MARCHANTIALES 13 



Class II. Anthocerotes. 



Gametophyte, a simple thallus, or sometimes showing a 

 trace of leaf-formation in Dendroceros; a single large chloro- 

 plast, containing a pyrenoid, in each cell; archegonium sunk 

 in the thallus, the antheridium endogenous; sporophyte large, 

 with long continued basal growth; sporogenous tissue derived 

 from the outer tissue (amphithecium) of the embryo. 



Class III. Musci (Mosses) 



The gametophyte shows a sharp separation into protonema 

 and gametophore. The protonema arises primarily from the 

 germinating spore, and may be either a flat thallus or more 

 commonly an extensively branching confervoid growth. 

 Upon this as a bud the gametophore arises. This has always 

 a more or less developed axis about which the leaves are 

 arranged in two, three, or more rows. A bilateral arrange- 

 ment of the leaves is rare, and the stems branch monopodially. 

 The asexual multiplication is by the separation of branches 

 through rhe dying away of the older tissues, or less commonly 

 by special buds or gemmse. Both stem and leaves have the 

 tissues more highly differentiated than is the case in the 

 Hepaticse. The archesporium is developed as a rule later 

 than is the case in the Hepaticas, and within is a large central 

 mass of tissue, the columella, which persists until the capsule 

 is ripe. In most cases there is a large amount of assimilative 

 tissue in the outer part of the capsule, and the epidermis at its 

 base is provided wnth stomata. The growing embryo breaks 

 through the calyptra at an early stage, and the upper part is 

 in most cases carried up on top of the elongating sporogonium. 

 In very much the greater number of forms the top of the cap- 

 sule comes away as a lid (operculum). 



THE HEPATIC^ 



The Hepaticse show many evidences of being a primitive 

 group of plants, and for this reason a thorough knowledge of 

 their structure is of especial importance in studying the origin 

 of the higher plants, as it seems probable that all of these 

 are derived from Liverwort-like forms. On comparing the 



