LINNEAN SPECIES IX OUR DAYS 295 



The self-iinpregnating wild plants are liomoz3^gous. If they are 

 occasionally impregnated by a foreign species, the former state will 

 be restored by degrees. I have cultivated thousands of individuals 

 and several hundred different forms of Capsella hiirsa-pastoris, and I 

 found almost all constant in several generations, 



Allogamous Wild Plants. 



Here T see a great danger for many Linnean species. The Men- 

 delists seem generally to assume that they must be heterozj'gous and 

 varying continually. If so, they do not correspond to any Linnean 

 species, and thus a large proportion of all species must be rejected. 

 Therefore it is necessary to examine earnestly the wild species that 

 are impregnated by insects or b}^ wind. As far as I know, the con- 

 clusion that these species must be heterozygous is verified only in a 

 few wild groups, e. g. Salix. 



If only a few allogamous species in a country be proved homo- 

 Z3'"gous, the conclusion that all are heterozj^gous should be withdrawn. 

 Clearly the existence of constant varieties within a species does not 

 pTOve a continuous formation of hybrids, nor does the appearance of 

 hybrid forms from new crosses. The hybrids must be produced by 

 the nature of the plant itself. One form may be homozygous in one 

 country, and the corresponding form in another country hetero- 

 zygous, if isolation and environment are different. 



Many heterozygous plants are easily mistaken as constant, espe- 

 cially if the obvious hybrids are few. Nevertheless, De Vries dis- 

 covered varieties of GLnotliera Lamarckiana even in natural growth. 

 He looked earnestly also for other species that were able to produce 

 " single variations." He cultivated numbers of such species, also 

 allogamous forms. But beyond (E". Lamarckiana he found all in the 

 " immutable period," and assumed that at Amsterdam most of the 

 wild species were immutable (Mutat. Theorie, i. p. 357). De Vries 

 found them in immutable period — that is to sa}^ constant. It will be 

 necessary to remind ourselves that wild plants have lived during 

 long periods ; (E. Lamarckiana, on the contrar}-, is probably a recent 

 product. 



Linne sowed very great numbers of plants, and always sought for 

 varieties. Some hybrids appeared, but all the species remained 

 constant. I think, therefoi'e, that Linne is right, as a rule, in assum- 

 ing that allogamous wild plants are also able to keep their character. 

 As I said above, he was reserved concerning some groups, and asked 

 for further research. 



The common fioras offer a kind of verification of the constancy 

 of man}^ wild plants, lieally there seems to exist a great number 

 of well-defined allogamous species. 



My own experience is not great, but I have observed most of our 

 Linnean species in their natuiul environment, and I also sowed 

 allogamous plants, such as Digitalis, Verhascum, Geum, Papaver, 

 (Enothera, etc. Never was I able to find varieties of a Linnean 

 species that I could presume to be hybrids produced by the sj)ecies 

 itself. 



