DIV. i BRYOPHYTA 475 



rangiferina is important as affording food for the Reindeer, and after the re- 

 moval of bitter substances can be used as fodder for cattle. Alcohol is obtained 

 from it in Norway. 



Some species particularly rich in Lichen acids are used in the preparation of 

 the pigments orseille and litmus ; there are in the first place species of Roccella 

 (especially R. Montagnei, . tinctoria, . fuciformis, and .K. phycopsis) which are 

 collected on the coasts of the warmer oceans, and the crustaceous lichen, Ochrolechia 

 tartarea, in North Europe and America. 



II. BRYOPHYTA (MOSSES AND LIVERWORTS) (*> 92 ' 93111 ) 



The Bryophyta or Muscineae comprise two classes, the Hepatkae or 

 Liverworts, aad the Musci or Mosses. They are as regards their 

 general segmentation Thallophyta, but are distinguished from them 

 by the characteristic structure of their sexual organs, ANTHERIDIA 

 and ARCHEGONIA, which are similar to those of the Pteridophyta. 

 The Bryophyta and Pteridophyta are accordingly, in contrast to the 

 Thallophyta, referred to collectively as Archegoniatae. 



The Bryophytes as well as the Pteridophytes reproduce also 

 asexually by means of SPORES provided with cell walls and adapted 

 for dissemination through the air. These two modes of reproduction, 

 sexual and asexual, occur in regular alternation, and are confined to 

 sharply distinct generations : a sexual (gametophyte), provided with 

 sexual organs, and an asexual (sporophyte), which produces spores. 

 The sexual generation arises from the spore, the asexual from the 

 fertilised egg. The number of chromosomes in the nuclei of the 

 sporophyte is t\vice as great as in the nuclei of the gametophyte. 

 The double number is acquired in the fusion of the sexual nuclei, 

 while the reduction to one-half takes place in the division of the 

 spore -mother- cells. This regular ALTERNATION OF GENERATIONS is 

 characteristic of all Archegoniatae. In the Bryophyta the plant is 

 the haploid generation, while the stalked capsule is the diploid 

 sporophyte. In the Pteridophyta the gametophyte is a small thallus, 

 w-hile the sporophyte is a large cormophytic plant. 



In the development of the SEXUAL GENERATION, the unicellular 

 spore on germinating ruptures its outer coat or EXINE, and gives rise 

 toa germ-tube. In the case of the Hepaticae the formation of the 

 plant at once commences, but in most of the Musci a branched, 

 filamentous PROTONEMA is first produced, composed of cells containing 

 chlorophyll (Fig. 432). The green, filamentous protonema gives 

 rise to branched, colourless rhizoids (?), which penetrate the sub- 

 stratum. The MOSS -PLANTS arise from buds developed on the 

 protonema at the base of the branches. Protonema and moss-plant, 

 in spite of the difference in appearance between them, together 

 represent the sexual generation. Many Liverworts possess a thallus 

 consisting of dichotomously-branching lobes (Figs. 446, 447), which 



