294 the journal of botany 



Mendelism. 



Fortunateh" we possess an authoritative work on Mendelism. 

 W. Johannsen, in his textbook {Elemente der e.vsal:fe?i Erhhch- 

 keitslelwe, ed. 2, 1913), presents the results with good criticism and 

 exact methods. From this I take the following points : — 



The Linnean species are reallj not units but embrace a various 

 number of "small species." These last must be the units in a 

 systematic natural history (p. 7). 



Yilmorin and MendeFs rule to cultivate each individuum apart is 

 necessary for analyzing the forms. This method gave excellent 

 results for the sugar industry, but has not been attended to by 

 scientists. The pure culture is as important in botany for studying 

 heredity as in bacteriology (p. 190). Botanists have too readily 

 described new species without cultivation. 



A pure line includes all individuals that descend from one homo- 

 zygous, self-impregnating individuum. The pure strains are quite 

 homozygous and seem to exist only among pure lines. The constancy 

 of the pure line persists until the homozygous nature is disturbed by 

 crosses or mutations (pp. 154, 627). 



Investigations concerning variability have shown three kinds of 

 variation : (1) pure phseno variation ; (2) geno-phaeno variation ; 

 (3) pure genovariation of the hybrids (pp. 7, 661). 



The idea of the character of species is dissolved. The characters 

 are not hereditary ; but the elements, the genes, are. Inheritance is 

 a genotypic phenomenon, its manifestations are eo ijpso pha3notypic 

 (pp. 628, QQd). The genotypic elements, the genes, are fixed and 

 immutable. It is unthinkable that a gene is a free living element. 

 The gene alone cannot produce anything. The whole genotypus 

 works all. Perhaps a moderate number of different genes are suffi- 

 cient for producing many biotypes (pp. 634, 667). 



So far, analysis by MendeVs methods is still in its initial stage. 

 Only the superficial features, not the'deeper organisation of the plants, 

 have been the object of study. We do not know whether we shall 

 ever be able to analyze species and genera (p. 668). 



Fate of the Constant Forms. 



How will the Linnean species prosper in the time to come ? I 

 think very well, as far as they are constant and limited by Nature. 

 Science interests herself in all Nature's works. The units or groups, 

 the natural families and' genera, as well as collective species and 

 constant varieties, will in all periods be subjected to researches, 

 especially in regard to their inter-relationship. Linne assumes that 

 in each natural group all the species and varieties are related, and are 

 descendants from only one species in the group. 



Generally all collective species, and also the well-defined constant 

 varieties that in culture still keep their character, can be called 

 Linnean species. Neither does there exist any difficulty in acknow- 

 ledging as species the apogamic constant forms and the asexual 

 constant strains. 



