President's Addhess — 8ect. J>. I" I 



ultra-Darwiniaiis, l.nt \>y sudden eliany,es, on wliieli naturtil selec- 

 tion then acts like a sieve whicli only allows suitable species to 

 pas.s. Do Vvies himselt" admits that mutations under observation are 

 as yet verj' rare, enouoh to indicate the possible and most probable 

 Avaj'S. but no more. He recoo-nises tliat many of the so-called species 

 of systematicists have to be split up into so-called elementary' species, 

 previously known as subspecies or tixed varieties. I do not think that 

 lie contributes to the clearness of the discussions on evolution and 

 heredit}' by thus giving a double meaning to the word species. 

 Either the species in the customary sense are elementary entities, or 

 they are not. If not, then the systematicists have to multiply their 

 species, however inconvenient such a procedure may l)e, and they maj' 

 recognise a position intermediate between the sub-genus and species, 

 which would then be taken up bj' what we call a species now. 



De Vries's nuitation theory is not bj^ anj^ means generally ac- 

 cepted. Time does not permit us to give an idea of the controversies 

 to wliich it has given rise, but I hope I have said enough to show that 

 if we want to make progress in our conceptions of the organic world, 

 species work, though not altogether on the lines of the old systemati- 

 cists, is required as a foundation on which alone a solid structine can 

 be" built. Ue Vries has rightlj- emphasised the fact tliat species are 

 not only the subject material of herbaria and similar collections, Imt 

 their life-history and life-conditions have to be studied in connection 

 with their external and internal morphological characters. 



The supposed gradual development of new species had been 

 deduced from two groups of observations, namely, the absence of 

 sudden or quick origin of new forms, and the principle of gradual 

 selection exercised by breeders of plants and animals. De Vries's 

 mutation theory is based on a number of facts which do not .seem to 

 be in agreement with the first gioups of observations, and latelj' he 

 has called attention to a method of selection of seeds which seems 

 furtlier to strengthen his conclusions. In \ iew of the practical 

 importance of this matter I will briefl}- deal with it. It is a well- 

 known fact that pedigree cultures are apt to deteriorate. Without the 

 introduction of fresh selected seeds niau}^ of our garden and field crops 

 constantly go back. This is the chief reason why British South Africa 

 imports annually about £40,000 worth of agricultural seeds. Add 

 to this sum mei'chants'' profits and other expenses, and it will be seen 

 that we are paj'ing rather a high price for keeping the strains of our 

 garden and field crops on a high level. The explanation of the 

 deterioration of so many high-class plants (e.g., rust proof wheats) 

 does not seem to lie mainly or exclusively in our climate, for the same 

 thing happens in the countries where high-class seeds are produced. 

 It seems that these seeds are usually mixtures of races, and unless 

 they are actually the descendants of a pure race which has originated 

 by mutation, there is no guarantee that the descendants will not vary 



