146 



SCIENCE. 



[N. S. Vol. XXIII. No. 578. 



enough for them to be incapable of breeding 

 together.' 



It will be readily apparent that it is ex- 

 tremely difficult to absolutely demonstrate a 

 case like that represented by the dotted lines. 

 Perhaps in no instance is the series of speci- 

 mens so complete as could be desired, and 

 usually it is not nearly adequate. The case 

 may be complicated by the existence of half 

 a dozen subspecies, occupying small areas, 

 justifying the nomenclature of the ' aspiring 

 young naturalist.' 



Last year I published a revision of Hy- 

 menoxys, a genus of plants (Bull. Torrey Bot. 

 Club, September, 1904). I found in that 

 genus a case which seemed to me to exactly 

 agree with those postulated by Dr. Allen, ex- 

 cept that the large form was southern, the 

 small one northern. The diiference between 

 the extremes was such as to almost constitute 

 a reductio ad ahsurdum of my classification; 

 yet when I had the whole series (borrowed, 

 from several large herbaria) spread out on a 

 table I did not know where to draw any hard- 

 and-fast lines. I accordingly called them all 

 subspecies of Hymenoxys chrysanthemoides, 

 but a comparison between plates 22 and 23 

 of my paper will doubtless cause many readers 

 to wonder how I could do it. 



Having myself attempted to demonstrate 



'■ Homo sapiens, who ofifers a classical example 

 of .segregation without physical barriers, is now be- 

 ing subjected to this very process. The result will 

 probably be greater racial uniformity, or rather 

 the breaking down of racial differences, with in- 

 creased individual variability, due to the fact 

 that while the individuals will cross, many of 

 their characters have become so far differentiated 

 that they will not do so. The mongrel dogs in 

 the street afford an illustration of this. How all 

 this will affect the development of the higher 

 human attributes, is a question which deserves 

 serious thought. The increase of insanity and 

 crime in civilized countries, though obviously due 

 largely to quite other factors, may be partly ex- 

 plicable as a result of incongruous combinations, 

 produced by ' Mosaic inheritance.' Genius, if 

 produced in good quantity, may become more 

 erratic. On the other hand, no doubt such evils 

 as war, famine and pestilence will be gradually 

 overcome, . r • , 



this case, I perhaps ought not to object to any 

 of Dr. Allen's; but all I wish to urge is, that 

 the evidence should be made more complete 

 and the different classes of cases should be 

 distinguished. In the case of the Hymenoxys, 

 we do not know what results would come from 

 sowing Texas seed in the vicinity of the City 

 of Mexico, and vice versa. Experiment might 

 show that while the characters of the herba- 

 rium specimens overlapped, there were in 

 reality several distinct plants, constitutionally 

 and essentially different, and that even most 

 of the apparent intermediates were really hy- 

 brids. Experiment might show, on the other 

 hand, that several so-called subspecies were 

 merely phases of one thing, the individuals 

 directly modified by the climate. This has 

 been demonstrated for certain mountain 

 plants, by dividing a single individual and 

 growing the halves at different altitudes. I 

 do not anticipate these results in the case of 

 Hymenoxys chrysanthemoides; but it would 

 be very well worth while to see whether they 

 are attainable. 



Finally, it is by no means to be assumed 

 that the ' effects ' of climate are necessarily 

 direct, and not brought about through the 

 agency of natural selection. This, however, 

 is a large question, not requiring discussion 

 at this moment. 



T. D. A. OOCKERELL. 



ONTOGENETIC SPECIES Al*D CONVERGENT GENEKA. 



The recent exchange of views in Science, 

 between Dr. Jordan and Dr. Allen concerning 

 ' environmental species,' gives occasion to 

 notice the widening gap between the formal 

 conception of species entertained by the biolo- 

 gisf as units of evolution, and the actual no- 

 tion of species used by the systematist in 

 working over a group, or the specialist in 

 arranging a collection. For if ' ontogenetic 

 species ' do occur, as there seems reason to 

 believe, a marked distinction must be made 

 in theory between them and the phylogenetic 

 species, as they might be termed, denoted by 

 the older, or Darwinian, definition which re- 

 quires the feature of inheritance of the char- 

 acters marking them. In practise, of course, 

 this feature has usually been taken for granted 



