222 THE NATURE AND ORIGIN OF LIFE 



them the associated, the other the dissociated state. It 

 seems likely that, as well from the morphogenic as from 

 other points of view, two such states will differ profoundly. 



It must also be remarked that, according to the con- 

 ditions, these two states may be derived hereditarily one 

 from the other. In fact, it would be enough that any cause 

 whatever should loosen the spring (cohesion, etc.) which 

 kept apart the two poles of each bipolar element ; and, be- 

 cause of the different morphogenic properties of the two 

 states, we should have a being B very different from a 

 being A and yet coming from it by direct heredity. 



Now such a phenomenon, precisely, is very general and 

 the two states which we have imagined the associated and 

 the dissociated state if they do not give us the real explana- 

 tion, at least furnish a possible model of the phenomenon 

 of alternating generation. 



Alternating generation is found in its simplest form in 

 ferns. 



A fern with leaves, such as we are accustomed to finding 

 along the wayside when autumn comes, has under its 

 leaves little brownish grains of Jiving substance in a state of 

 latent life. They are spores or reproductive elements which 

 have not undergone sexual maturation. But, while they 

 have not undergone such maturation, they have at least 

 experienced a modification in their state ; for they germinate 

 and produce, not a leafy fern like that which gave birth to 

 them, but a formless cellular mass resembling a green sea- 

 weed and called prothallus. 



In the prothallus later on there appear sexual elements 

 properly so-called, male and female, whose union gives eggs 

 which reproduce the leafy fern. This closes the cycle 

 of an obligatory alternating generation. 



It is plain that such alternating generation is related with 



