236 THE SIMPLEST LAND PLANTS 



spirally coiled body of the sperm consists almost 

 wholly of nucleus, with a little colourless cytoplasm 

 at the front end to which the flagella are attached 

 (Fig. 37, B). The sperm cell is here reduced to its 

 lowest limits — the paternal nucleus and the flagella, 

 which are the means of carrying the nucleus to the egg. 



The female organs are formed in groups, overhung 

 by a membrane which grows out from the thallus 

 behind them. They are flask-shaped, and in each 

 there is a single egg contained in the body {venter ^) 

 of the flask, which it practically fills (Fig. 37, C). The 

 neck of the flask is composed of a single layer of cells 

 continuous with those forming the wall of the venter. 

 There is open communication from the egg to the 

 exterior through the channel of the neck, which is 

 filled with mucilage. This flask-shaped type of female 

 organ, which is characteristic of the Liverworts and 

 Mosses and also of the lower vascular plants (Pteri- 

 dophyta), is called an archegonium. 



When a film of water (rain or dew) is present on 

 the surface of the thallus the ripe antheridium opens 

 by the swelling and bursting of its wall and thus sets 

 free the sperms, which are attracted to the mouth of 

 the archegonium by the secretion of a substance, prob- 

 ably cane sugar, produced by the latter and diffusing 

 out into the water. On reaching the mouth the 

 sperms become entangled in the mucilage, wriggle 

 down the neck and one of them fuses with the egg, 

 which then becomes a zygote and secretes a wall. 



The egg of Pellia (Fig. 37, C) is much smaller than 

 that of Fucus, and this is related to the fact that it is 

 not cast out from the thallus, and does not, therefore, 

 have to depend on its own resources during germi- 



' Belly. 



