188 



an embryo consisting of a very small stem-portion and a terminal spore-pro- 

 ducing leaf. This will be further explained in the introduction to the Flower- 

 ing-plants (p. 236). 



In the Liverworts the young sporogouium lives like a parasite, 

 being nourished by the sexual generation (only in Anthoceros has it 

 a slight power of assimilation). In the Leafy- Mosses, on the other 

 hand, with regard to the power of assimilation, all transitions 

 are found from abundant assimilation (Funaria, Physcomitrium') 

 to almost complete " parasitism " (Sphagnum, Andrecea). In the 

 majority of the operculate Mosses the sporogonium has a more 

 or less perfect system of assimilation, and is able itself to form a 

 large portion of the material necessary for the development of the 

 spores, so that it chiefly receives from the sexual generation the 

 inorganic substances which must be obtained from the soil. The 

 more highly developed the assimilative system of the sporogonium, 

 the more stomata are present. 



APOSPORT. In some operculate Mosses it has been possible to obtaiu a pro- 

 tonema with small Moss-plants from the seta, when severed from its Moss- 

 pls,nt, and grown on damp sand. 



The Mosses are the lowest plants which are provided with stem 

 and leaf. They are assigned a lower place when compared with 

 the higher Cryptogams, partly because there are still found within 

 the Division so many forms with a mere thallus, partly because 

 typical roots are wanting and the anatomical structure is so ex- 

 tremely simple, and partly also because of the relation between 

 the two generations. The highest Mosses terminate the Division, 

 the Muscineas and Pteridophyta having had a common origin in 

 the Algae-like Thallophyta. 



They are divided into two classes : 



HEPATIC^;, or Liverworts. 



Musci FKONDOSI. True Mosses or Leafy-Mosses. 



Class i. Hepaticae (Liverworts). 



The protonema is only slightly developed. The remaining part 

 of the vegetative body is either a prostrate, often dichotomously- 

 braiiched thallus, pressed to the substratum (thalloid Liverworts), 

 with or without scales on the under side (Figs. 194, 197) ; or a 

 thin, prostrate, creeping stem, with distinctly-developed leaves, 

 which are borne in two or three rows (Figs. 195, 198), viz., two on 

 the upper and, in most cases, one on the under side. The leaves 

 situated on the ventral side (amphigastria) are differently shaped 

 from the others (Fig. 198 a), and are sometimes entirely absent. 



