60 TIIK JOl'KNAL OF BOTAXT 



]>uritv. Tliei-e are, for instance, two kinds of white mice externally 

 indistinguislial)le and reproducing their kind faithfully and vet of 

 different constitution, as is shown hy mating a female of each kind 

 with the same black male. In one case the offspring will be 

 uniformly black, in the other unifonnly grey. Hybrid analysis is 

 necessary to detect these constitutional ditt'erences, and hence we can 

 define a species as " the total of individuals of identical constitution 

 unable to form more than one kind of gamete." Unfortunately 

 there is no absolute test for a " species," and further, such s])ecies are 

 very mre in Nature. The botanist who has been in the habit of 

 regarding the old style species as a unit for purpose of his work will, 

 however, be comforted to hear that while neither the Lin neon nor the 

 Jordanon re])resents the ultimate organic atom, yet that these groups 

 of individuals are natural. " It is Nature itself," says Dr. Lotsy, 

 " which groups the individuals to Linneons, and Linneons are thus 

 something more than mere conceptions of the human mind." A 

 Linneon is a group of individuals of different constitutions, which 

 is merely a vestige of a very large number of types which spring 

 from a cross. Intercrossing has taken place within the Linneon, and 

 by selection has resulted in a certain uniformity of appearance which 

 then characterizes the Linneon. Linneons, though themselves the 

 result of a cross, are ke])t distinct in nature by obstacles against their 

 freely crossing with other Linneons. Hence, at any rate, the members 

 of any one Linneon have a common origin. Further, the degree of 

 variability which the botanist recognizes within the limit of the 

 s])ecies (O.S.) is explained from Dr. Lotsy's point of view by the 

 constant occurrence within the Linneons of new forms resulting from 

 intercrossing. The species (N.S.) or ultimate unit remains, like the 

 constitution of the gamete, very much in n/fhibus, where, we fear, the 

 systematist, at any rate, will be constrained to leave it. 



Dr. Lotsy is severe on mutations. In his chajjter " Do diploid 

 species vary ? " he claims that, while it is not inconceivable, there is 

 no evidence that a homozygous individual can become heterozygous 

 without having been crossed, and this is what is implied in mutation. 

 We cannot be sure of the homozygous condition, that is of the specific 

 purity, of the material from which the supposed mutants arise ; 

 (Enothera Lamarckiaiia, for instance, has never been obtained in 

 a homozygous condition. 



New species arise from a poh^gametic hybrid obtained by mating 

 gametes of different constitution, which are brought together by 

 crossing different s]>ecies. The polygametic hybrid thus obtained 

 gives rise to new forms, some of which are heterozygotes, while others 

 are homozygotes, that is new species. By isolation of such homo- 

 zygotes in the experiment ganlen and b}^ selfing them or by mating 

 them with other individuals of identical constitution, but of different 

 sex, we can nndtiply them and thus obtain new species consisting of 

 as many individuals as we choose to raise. It is not necessary that 

 the gametes which unite to give rise to the polygametic hybrid should 

 be derived from ]Kn'e species ; they luay equally well be derived from 

 hybrids, as it is tlie constitution, not the origin, of these gametes which 

 is of conscfjuencc. Hence new s]x'cies mny ori^-inalc polvjiliylctical^v. 



