II MUSCINE^—HEPA TICyE—MARCHA NTIA CE^ 1 3 



Class II. 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 arrangement of the 

 leaves is rare, and the stems branch monopodially. The 

 asexual multiplication is by the separation of branches through 

 the dying away of the older tissues, or less commonly by 

 special buds or gemmae. Both stem and leaves have the 

 tissues more highly differentiated than is the case in the 

 Hepaticae. The archesporium is developed as a rule later 

 than is the case in the Hepaticae, 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 with 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 

 capsule comes away as a lid (operculum). 



The Hepatic(E 



The Hepaticae 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 

 Hepaticae with the Mosses one is at once struck with the very 

 much greater diversity of structure shown by the former group, 

 although the number of species is several times greater in the 

 latter. On the one hand, the Hepaticae approach the Algae, 

 the thallus of the simpler forms being but little more compli- 

 cated than that of many of the higher green Algae. On the 

 other hand, these same simpler Liverworts resemble in a most 

 striking manner the gametophyte of the Ferns. The same 



