ANTHERIDIA OF PELLIA 277 



obscures the green colour of the living ones, and causes the whole 

 plant to appear whitish. The Moss Leucobryum, common on 

 wet heaths, possesses leaves with a somewhat similar structure. 



Both Liverworts and Mosses propagate abundantly by vege- 

 tative means, most frequently by fragmentation of the thallus. 

 In many Liverworts, and some few Mosses, the thallus forms 

 special bodies called gemma, which consist of a varying number 

 of cells and are often of characteristic shape (Fig. 149, D). In 

 Marchantia they are formed in special cup-like outgrowths on 

 the upper surface of the thallus (Fig. 146, E, g.), but in the 

 leafy Liverworts they are usually budded off from the tips of 

 the shoots. An abundant production of gemmae is likewise seen 

 in the Moss Aulacomnion androgynum, where they arise in a 

 spherical cluster at the top of the stem. 



The ordinary Moss or Liverwort plant, however, also re- 

 produces by sexual means, the sexual organs developing especially 

 in the early spring. Their general character, in the case of 

 Liverworts, will be gathered from an examination of Pellia. 

 The male organs are found in the region of the midrib, and are 

 visible to the naked eye as a number of dark pimples, each of 

 which, in a vertical section (Fig. 152, A), is seen to correspond 

 to a single more or less spherical antheridium. The latter 

 (Fig. 152, B) is borne on a very short stalk, and almost fills a 

 flask-shaped depression in the thallus which communicates with 

 the exterior by a narrow pore. 



The antheridium possesses a wall (Fig. 152, B, w.) which is 

 composed of a single layer of cells, and at maturity encloses 

 numerous small, colourless, closely packed spermatozoid mother- 

 cells, each producing a single spermatozoid (Fig. 152, D). 

 Through vigorous absorption of water, in wet weather, by the 

 cells of the wall, the apex of the antheridium is ruptured, and 

 the mucilaginous mass of mother-cells is discharged into the 

 surrounding moisture. Here occurs the final liberation of the 

 spermatozoids, each of which possesses a spirally coiled body 

 (formed mainly from the nucleus of the mother-cell), bearing 

 two long cilia at the slightly tapering front end (Fig. 152, C) ; 

 a small vesicle, representing the remaining cytoplasm of the 

 mother-cell, is generally seen at the opposite end, but is shed 

 during movement. 



