BRYOPHYTA 133 



with all Mosses. The two sexes are quite distinguish- 

 able by the habit of the plants. The male plants are 

 of fair size, reaching a centimetre in height ; in the 

 lower part of the stem the leaves are scattered, but at 

 the top they are crowded together to form a conspicuous 

 rosette. This is not unlike a flower, especially as the 

 middle part of the rosette is of a reddish colour. In 

 some of the larger Mosses (such as Polytrichum, which 

 includes the very large Moss so common on heaths) 

 the resemblance to a flower is still more striking. 

 However, there is of course no direct homology. for these 

 rosettes belong to the oophyte, not to the sporophyte 

 generation, and the organs which they enclose are anthe- 

 ridia, not stamens. On the growing-point, within the 

 rosette, numerous antheridia arise in long-continued suc- 

 cession without any strict order. Both young and mature 

 antheridia are shown in Fig. 61. As usual, the 

 antheridium owes its origin to a single cell in which 

 one or two transverse walls are formed, after which 

 the growth goes on entirely by means of the apical 

 cell, which cuts off two rows of segments. It is a good 

 general rule in the Mosses that every organ, of whatever 

 kind, grows by means of an apical cell, whereas this 

 mode of growth is nothing like so general among the 

 Liverworts. By further subdivisions of the segments, 

 and finally of the apical cell itself, the antheridium is 

 differentiated into an external wall one cell in thickness, 

 and an internal mass of small-celled tissue, each cell 

 of which becomes the mother-cell of a spermatozoid 

 (Fig. 61, J). 



The mature antheridium is club-shaped and reaches 

 0'3 millimetre in length, containing an enormous number 

 of mother-cells. The development of the spermatozoid 



