172 REPRODUCTION 



In certain cases the prothallus is unisexual, that is to say, 

 unUke the prothaUus of the bracken-fern it has either male 

 or female gametes but not both. In that case the spores which 

 give rise to the prothallus may differ in size. The larger, or 

 megaspores, grow into the female prothallus ; the smaller, or 

 microspores, into the male prothallus. In the fern, the spore 

 that gives rise to the gametophyte separates away from the 

 body of the sporophyte (i.e. the flourishing green plant known 

 as the fern). But as certain medusae or jelly-fish will not 

 separate away from their hydroid stock, so the gametophyte 

 and the sporophyte may continue in contact all their life. 

 In the moss, the gametoj)hyte is the dominant organism; 

 it is in fact the moss plant with its tiny leaves, etc., but it 

 embraces the sporophyte or capsule which remains embedded 

 in the body of the former. Perhaps it is in mosses that the 

 gametophyte reaches its best, for in the higher plants the 

 gametophyte totally fails to make good. It is dominated and 

 surpassed by the sporophyte, as is, of course, very obvious 

 in the fern. This is still more obvious in the seed-bearing 

 flowering plants. The pollen sacs in the anther which pro- 

 duces the pollen grain are the microsporangia, and the pollen 

 represents the microspores. The nucellus in the female flower 

 is the megasporangium and the embryo-sac is the megaspore 

 which after fertilization will give rise to the new plant, the 

 sporophyte. 



Mosses and ferns at the most critical part of their life, that 

 is when the fertilization of the egg is taking place, must have 

 moisture; the antherozoids cannot move in the air — they 

 must swim. In a way, these plants are the amphibia of the 

 vegetable world; just as the frog has to descend into the pond 

 to spawn, or a land crab into the sea, so mosses and ferns 

 must have a certain amount of water for their male cells to 

 smm towards the ova. A modern poet has written : 



Magnificent out of the dust we came 

 And abject from the Spheres. 



But I do not think the modern poet has made any deep study 

 of the subject. The general consensus of opinion is that the 

 land flora and fauna came from the waters. 



