424 GEOGRAPHICAL DISTRIBUTION [CHAP. VI 



Letter 325 pp. 503-514) on the relation of the size of families to the 

 average range of the individual species ; I cannot but think, 

 from some facts which I collected long before De Candolle 

 appeared, that he is on wrong scent in having taken 

 families (owing to their including too great a diversity in the 

 constitution of the species), but that if he had taken genera, 

 he would have found that the individual species in large 

 genera range over a greater area than do the species in 

 small genera : I think if you have materials that this would 

 be well worth working out, for it is a very singular relation. 



With respect to naturalised plants : are any social with 

 you, which are not so in their parent country ? I am surprised 

 that the importance of this has not more struck De Candolle. 

 Of these naturalised plants are any or many more variable in 

 your opinion than the average of your United States plants ? 

 I am aware how very vague this must be ; but De Candolle 

 has stated that the naturalised plants do not present varieties; 

 but being very variable and presenting distinct varieties seems 

 to me rather a different case : if you would kindly take the 

 trouble to answer this question I should be very much obliged, 

 whether or no you will enter on such points in your essay. 



With respect to such plants, which have their southern 

 limits within your area, are the individuals ever or often 

 stunted in their growth or unhealthy ? I have in vain 

 endeavoured to find any botanist who has observed this 

 point ; but I have seen some remarks by Barton on the 

 trees in United States. Trees seem in this respect to 

 behave rather differently from other plants. 



It would be a very curious point, but I fear you would 

 think it out of your essay, to compare the list of European 

 plants in Tierra del Fuego (in Hooker) with those in North 

 America ; for, without multiple creation, I think we must 

 admit that all now in T. del Fuego must have travelled 

 through North America, and so far they do concern you. 



The discussion on social plants (vague as the terms and 

 facts are) in De Candolle strikes me as the best which I have 

 ever seen : two points strike me as eminently remarkable in 

 them ; that they should ever be social close to their extreme 

 limits ; and secondly, that species having an extremely con- 

 fined range, yet should be social where they do occur : I 

 should be infinitely obliged for any cases either by letter or 



