SECT. I CRYPTOGAMS 425 



cells, the proeiiibryo. From the iirst node of the proenibryo rhizoids arc produued, 

 while at the seeond node there arise, together with a lew simple lateral axes, one 

 or more main axes, which finally develop into a full-grown plant. 



Chara crinita, only female plants of which occur in Europe, is remarkable in 

 tliat the egg-cells develop parthenogenetically {i.e. without being fertilised) into 

 oospores. These, omitting the reduction division, give rise to purely female sexual 

 plants. 



The formation of tuber-like bodies (bulbils, starch-stars) on the lower part of 

 the axes is characteristic of some species of the Characeae. These tubers, which 

 are densely filled with starch and serve as hibernating organs of vegetative repro- 

 duction, are either modified nodes with much-shortened branch whorls {e.g. in 

 Tobjpellopsis stclligera, when they are star-shaped), or corres}>ond to modified 

 rhizoids {e.g. the spherical, white bulbils of Chara as2)cra). 



II. BRYOPHYTA (MOSSES AND LIVERWORTS) (102, 103, i04) 



The Bryophyta or Mnscineae comprise two classes, the Hepaticae 

 or Liverworts, and the Musci or Mosses. They are distinguished 

 from the Thallophyta 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 Arcliegoniatae. 



The Bryophyta as well as the Pteridophytes multiply also 

 asexually by means of spores provided with cell walls and adaj^ted 

 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 twice 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. While in the Bryophyta the 

 plant is the haploid generation, in the Pteridoplij'ta the plant is 

 diploid. 



In the development of the sexual generation, the unicellular 

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

 to a germ-tube. In the case of the Heimticae, 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. 3G5, r). The green, filamentous protonema gives 

 rise to branched, colourless rhizoids (r), 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 



