rn- 



i 



560 



THE BEGINNINGS OF LIFE. 



_-*. "^ 



persist. That is to say, whilst they are individually 

 short-lived, and are most prone to give birth, at dif. 

 ferent times, to other organisms of the most varied 

 nature, they are also exceedingly apt to recur, quite 

 independently, just as certain crystalline forms are apt 

 to recur, when crystallizable compounds separate from 

 the state of solution, at different periods. 



Ephemeromorphs and ^ Alternate Generation.^ 



The studies which have revealed some of the nu- 



r 



merous and complex relationships existing between 

 the multitudinous varieties of ^ Ephemeromorphs,' have 

 been of cardinal importance for the science of Bio- 

 logy. They have taught us, not only that living matter 

 is formable de novo^ but that it possesses inherent ten- 

 dencies of such a nature as to make it prone to undergo 

 variations in constitution, directly leading to variation 

 in external form^ that transitions are always easy in 

 these early stages from the simpler vegetal to the 



more complex animal modes of growth, and vice 



under 



versa j 



and thatj in the main, when placed 



favourable conditions, the different forms tend to 



Lichens as Lecidea geograpbica probably date from almost fabulous 

 periods, and even small patches are often of considerable age, I have 

 myself watched individuals for twenty-five years, which are now much 

 in the same condition as they were when they first attracted my notice. 

 Plants which endure without injury such extremes of temperature, and 

 conditions of the hygrometer, would seem, a priori, to be likely to nave 

 great powers of longevity.' ('Introd. to Crypt. Bot.,' p. 418.) 



iduor 



) 



will form 

 So thai 



the pare 

 tiious process 

 tot the spore o 

 of tends again t 

 is may be se 

 conidium or spi 

 it had S( 



s has be 



er 



occurrence 



^l heteroo 

 f« off from th 



ion 



( 



5 



^'OL. 



II. 



