CONCLUSION 297 



In another genus of green fresh-water algae, Coleo- 

 chcete, the oospore, while still enclosed in the oogonium, 

 divides up into a cellular tissue, in each cell of which 

 a zoospore is formed. This process shows a certain 

 analogy with the formation of the simplest forms of 

 sporogonium in the Liverworts, among which there is a 

 genus (Riccia] in which the fruit consists of nothing but a 

 mass of spore mother-cells surrounded by an epidermis. 

 There is, however, a very wide gap between the Alga and 

 the Hepatic. In the Alga in question the asexual spores 

 produced by the oospore are identical with those formed 

 on the vegetative plant ; whereas in even the lowest 

 Bryophytes the spores are never formed anywhere else 

 than in the sporogonium. 



The sporophyte of the higher plants, whatever its 

 origin may have been, is specially adapted to the 

 formation of aerial, as distinguished from aquatic, spores. 

 The spores of the Archegoniatse, from the lowest 

 Bryophyta upwards, differ from those of any of the Algre 

 in being almost always suited for dissemination by the 

 air. The sporophyte which bears them is essentially the 

 aerial generation, while the oophyte is dependent on 

 water for the act of fertilisation. The difference is very 

 well shown in Pellia, where the sexual generation is a low- 

 growing thallus, keeping close to the damp ground, or even 

 living under water, while the sporophyte grows up high 

 into the air, exposing its spores as freely as possible, so 

 that they may be dispersed by the wind. The result in 

 other cases is attained in a different way, but the general 

 rule holds good, that the function of the sporophyte the 

 dissemination of spores requires exposure to dry air, 

 while the most important function of the oophyte the 

 act of fertilisation requires the presence of water. 



