96 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



of every outside agent there generally is an increase in 

 the rate of development corresponding to the increase of 

 intensity of the agent. The acceleration of development by 

 heat has been shown to follow the law of the acceleration of 

 chemical processes by a rise of temperature ; that seems to 

 prove that certain chemical processes go on during the 

 course of morphogenesis. 



Almost all that has been investigated of the part played 

 by the external conditions of development has little bearing 

 on specific morphogenesis proper, and therefore may be left 

 out of account here : we must, however, lay great stress 

 on fhe general fact that there is a very close dependence 

 of morphogenesis on the outside factors, lest we should be 

 accused afterwards of having overlooked it. 



Of course all " external " means or conditions of morpho- 

 genesis can actually relate to morphogenetic processes only by 

 becoming in some way " internal," but we unfortunately have 

 no knowledge whatever how this happens. We at present 

 are only able to ascertain what must necessarily be 

 accomplished in the medium, in order that normal morpho- 

 genesis may go on, and we can only suppose that there 

 exist certain specific internal general states, indispensable 

 for organogenesis but inaccessible to present modes of 

 investigation. 1 



The Discoveries of Herbst. There are but few points 

 in the doctrine of the external means or conditions of 

 organogenesis which have a more special bearing on 

 the specification of proper form, and which therefore 



1 Compare the analytical discussions of Klebs, to whom we owe a great 

 series of important discoveries in the field of morphogenetic "means" in 

 botany. ( Willkurliche Entwickelungsdnderungen bei Pftanzen, Jena, 1903 ; 

 see alsoBiol. Centralblatt, vol. xxiv., 1904, and my reply to Klebs, ibid. 23, 1903.) 



