Wall. — Ranunculus paucifolius T. Kirk. 105 



Postscript. 



This paper has been submitted to Professor Hugo de Vries, and he has 

 sent me this comment : — 



" It is, of course, interesting for me to read a statement of my views 

 from a neo-Lamarckian standpoint, and the concession that the facts 

 described by you do not contain any argument for a decision between 

 the two contrasting theories. i 



" For me your article shows that R. 'paucifolius, R. chordorhizos, R. 

 crithmifolius, and R. Haastii must have had a common ancestor, which 

 was already a xerophyte, and that they must have inherited this character 

 from it. This ancestor may have had the same geographical distribution 

 which is now shown by the aggregate of its descendants. Perhaps one 

 of them is identical with it ; perhaps it has wholly disappeared. Under 

 what conditions it lived we can, of course, not know, nor where and when 

 it acquired its xerophytic properties. To conclude that it must have 

 acquired them in a period of drought would be a circulus vitiosus, since it 

 would simply be applying the theory to a special case and then considering 

 the case as a proof of the theory. 



" You say that possibly new characters may be acquired by a plant 

 as a direct response to Nature's ultimatum, ' Change or die.' This is the 

 old view, but not mine. The article you quote from was just intended 

 to show that, as far as we know, the response has, as a matter of fact, 

 always been, ' I cannot change at your will and so I must die.' 



" You assume that your plants have passed through periods of moisture, 

 but have retained their xerophytic character nevertheless. It seems to me 

 that this is conceding that external conditions do not, as a rule, provoke 

 corresponding useful changes. They may do so, or seem to do so, or they 

 may not. My view, that mutations, although, of course, caused by external 

 conditions, are not necessarily responses to the ' demands of a new stress,' 

 seems quite adequate to interpret your facts. I gladly concede that the 

 causes of mutations are still dark to us, but then I say that responses such 

 as Warming and other neo-Lamarckians suppose are far darker. Especially 

 if you take into consideration what is now known concerning the structure 

 of chromosomes and the distribution of the hereditary characters in them, 

 it seems impossible to imagine the nature of such a supposed response. On 

 the other hand, if we do not know the cause's of mutation, the fact of 

 their occurrence has been proved in so numerous individual cases that it 

 can no longer be doubted, even by those who want to exclude the Oenotheras 

 from the discussion. 



" I shall be very glad to learn the results of your garden cultures. 

 I should not wonder if your plants would behave just like the creosot- 

 bush of Tucson, and prefer better conditions to those which they enjoy (?) 

 just now. To me it seems that plants are found in those localities where 

 they can better endure the circumstances than their competitors. But 

 whether they really enjoy them, or would prefer more moisture and more 

 fertile soils, and so on, is another question." 



