The Origin of Species 335 



some connection between the conditions of life in 

 fresh water and the evolution of sexual cells. This 

 may, perhaps, be sought in the necessity for most 

 fresh-water plants to provide resting stages. The 

 zygote resulting from the union of two small, similar 

 gametes is provided with a smaller amount of food 

 material than is the case where there are well-de- 

 veloped sexual cells, large eggs and small sperms. 

 Moreover, the larger amount of contents in such a 

 large spore allows for a greater number of spores 

 on germination, and so might be an advantage. 

 Whether the fusion of the gametes provides a 

 greater store of energy as well, can hardly be 

 proven, but it is not at all unlikely. It is thus quite 

 conceivable that the need for a resting stage fitted 

 to produce quickly a number of germs at the end 

 of the dormant period, was the most important 

 factor in the specialization of the sexual cells in 

 the fresh-water algae. The futher evolution of the 

 zygote, as shown in the highly complex sporophyte 

 of the terrestrial plants, has been sufficiently dwelt 

 upon in an earlier chapter. The absence of any 

 need for the terrestrial resting stage in the green 

 and brown seaweeds may, perhaps, explain the gen- 

 erally low type of sexual cells in these forms. 



The peculiar type of reproduction in the red algae 

 has evidently arisen quite independently, and the 

 peculiar spore fruit has its nearest analogy in that 

 of certain fungi. It will be noted that in the red 

 algae also, the fertilized cell does not produce new 



