lotsy's theory of evolution. 265 



be those in which the species most easily hybridise. I doubt 

 wliether this is so, although the European flora seems to afford 

 good examples to make this supposition probable. 



Secondly, genera in which cross-breeding in a state of 

 nature is of frequent occurrence should show few well-defined 

 species. It is, e.g., a well-known fact that one cannot breed 

 aloes true in South x'Vfrica or in countries where they can be 

 grown in the open, when you have a number of species close 

 together and natural hybrids are also common, yet a large 

 numljer of species which grow under conditions where hybridi- 

 sation is possible have, to our certain knowledge, persisted as 

 far as our knowledge of them goes back. The same applies to 

 Stapelias. I have purposely refrained from touching on 

 zoological evidence that may be brought forward against Lotsy's 

 theory. But I think I have said enough to show that while I 

 am far from asserting that hybridisation may not be one of the 

 factors which have brought about evolution, I cannot admit that 

 Lotsy's theory has brdugln us nearer the knowledge of the 

 vera causa of evolution. This is still, as S. Laing would have 



said, A PROBLEM OF THE FUTURE.* 



Drought in the WateRBERG.— The Annual Re- 

 port of the Smithsonian Institution, Washington City, U.S.A., for 

 1914, just received, contains, by special permission, a reprint, iit 

 extenso, of an article by Adv. E. N. Marais, of Rietfontein, 

 Waterberg, taken over from the .-l(/ricii!titral Journal of the 

 Union of South Africa,'' and entitled " Notes on some effects of 

 extreme drought in AA'aterberg, South Africa." 



* The very interesting ovarial treatment of Scrophiilaria by McDougal 

 with a dilute solution of potassium iodide which yielded two aberrant 

 individuals deserves great attention in connection with the matter under 

 discussion, especially as evidence has been produced by F. E. Lloyd that 

 the reagent penetrates to the egR-apparatus. It is too early yet to base 

 and definite conclusions on the results, though carried alreadv to the F- 

 generation. However, the changes produced are not premutational or 

 cumulative, but are induced by direct physico-chemical action. They 

 seem to show that " some departures might be evaluated as losses of 

 characters, others are increased differentiations," which of course Lotsy 

 would explain as more or less dormant " genes '" let loose. 



See ■' Yearbook of the Carnegie Institution of Washington,'' 13 

 (1914), 77-81. 



