FUNCTION AND ENVIRONMENT 198 



living creatures from their surroundings. 

 To do so in fact is to kill them; to do so in 

 theory is to turn biology into necrology, a 

 vice which has always too largely infested 

 our science, paralyzed its thinkers, sometimes 

 even skeletonized or mummified them. There 

 is an endless diversity in environments, and 

 some of them are most extraordinary the 

 iceberg, the hot spring, the mountain top, the 

 abysses of the ocean, the cave, the interior 

 of another creature but for each kind of 

 organism there is an indispensable minimum 

 of supplies and influences, apart from which 

 it cannot develop, or grow, or continue to 

 live. This is the fundamental relation of 

 living things, that of constant and normal 

 environmental dependence. 



(2) But surroundings are changeful and the 

 living creature changes with them. In many 

 cases, where the external changes are regularly 

 recurrent, like seasons and tides, the organism 

 falls into step with them; so that there are 

 internal rhythms, punctuated by external 

 periodicities. The latter may come to be 

 needed only as the liberating stimuli, or 

 trigger-pullers, of the former. Experiments 

 show that some young tropical acacias are 

 hereditarily wound up, as it were, to a twelve 

 hours' day and night times of leaf -expansion 





