FERTILIZATION IN PLANTS AND UNICELLULAR ORGANISMS 331 



appear to us quite unintelligible, since we should be aware that in 

 these also the fire of life is continually being fed by the supply of 

 new combustible material. Not the potential immortality of uni- 

 cellular organisms would then appear to us remarkable and surprising, 

 but the limitation of the life of multicellular organisms— the occurrence 

 of natural death. Who knows whether, in that case, many of those 

 investigators trained in regard to unicellular organisms alone would 

 not say just the opposite of what Biitschli has said, that there could 

 be no natural death in many-celled organisms, since single-celled 

 organisms prove to us that life is an endless chain of transitory 

 minute vital units ? 



Furthermore, our physiologists are still far from being able to 

 explain the natural death of many-celled organisms from below — 

 I mean from a knowledge of its necessary causes; on the contrary, 

 they argue from the known occurrence of natural death to the causes 

 which underlie it ; and thus they have arrived at the idea, undoubtedly 

 correct, that the somatic cells of the body are gradually so altered by 

 their own activity that they are ultimately unable to function any 

 longer and must die off. Therefore, if we were unacquainted with 

 death, we should not have been able to infer it from our physiological 

 knowledge, and still less from our knowledge of the unicellulars. 



As our insight has in point of fact grown by starting from the 

 mortal many-celled organisms, and has only later penetrated down to 

 the unicellular organisms, so we can understand the genesis of the 

 conclusion, deduced from the mortality of the many-celled organisms, 

 that unicellular organisms also are unable to continue without limit 

 the renewal of material and of vital particles, and that consequently 

 they would be subject to natural death if nature had not found in 

 conjugation a ' remedy ' for ' the physiological difficulties which ensue 

 automatically and necessarily from the constitution and from the 

 continual functioning ' even of unicellular organisms. 



But we ask in vain for a shadow of proof of this remarkable 

 conception ; it is an axiom deduced from our knowledge of natural 

 death among multicellular organisms, and bolstered up by a mistaken 

 application of the idea of ' perpetual motion.' Or may we regard it 

 as a proof of this if it should be found that all unicellular organisms 

 are adapted for conjugation? 



We shall see later on that amphimixis has certainly quite a 

 different and, undoubtedly, a very important effect, namely, that it 

 increases the capacity of the species for adaptation; and a life- 

 renewing effect in Butschli's sense could only be ascribed to it in 

 addition if the assumption of the necessity of a natural death in 



