146 Varietäten. Descendenz, Hybriden. 



der of the Darwinian opinions, the author takes some quotations, 

 indicating the great value, of discontinuous variations in Huxleys 

 opinion. Whenever Huxley expressed himseif on this matter he 

 usuall}' took occasion to say explicitly that he could see no reason 

 why variations should not be discontinuous as well as continuous, 

 and one of the few points on which he differed from Darwin was 

 in ascribing greater significance to such marked changcs. The Sta- 

 tements ar to be found in Huxleys volume of essays, entitled Dar- 

 winiana, (p. 39, 77, 97, 181, 223). From these and similar Statements 

 it appears evident that were Huxley living to day, he could scar- 

 cely escape being classed as a mutationist. M. J. Sirks (ßunnik). 



Holden, R., Hybrids of the genus Epilobium. (American Natu- 

 ralist. L. p. 243—247. 1916.) 



The relationship between h3'^bridism and failure of pollendeve- 

 lopment, defended by Jeffrey, was founded especially upon the 

 sanity of pollen in anthers of Epilobium angustifoliu.ni, the only 

 species of the section Charnaenerion , that does not hybridize with 

 the many species of the section Epilobium s.str., as E. montanutn^ 

 E. parviflorum and E. hirsutum. In the southern pans of North 

 America E. angustifolium showed sound pollen, but the other 

 species a great many shrivelled anthers and sterile pollen. 



But among the individuals of E. angustifolium, found in Eng- 

 land, there are a great many with partially sterile pollen, as Miss 

 Holden found. These facts seemed to invalidate the conclusion 

 that abortive spores are an invariable sign of hybridism, but, as 

 has so offen been the case in scientific matters, evidence which at 

 first seems to descredit a given hypothesis, on further investigation 

 is Seen actually to corroborate the same hypothesis. For the indi- 

 viduals of E. angustifolium in England which had partially sterile 

 pollen, belonged to two different varieties of this species: E.macro- 

 carpum (Steph.) and E. brachycarpum (Leight.). Wherever these 

 two varieties are present, the spores are partially abortive. This 

 State of affairs is found in England, and probably in Europe, 

 Asia and western North America, where both varieties are 

 known to exist. Wherever on the other band, as in southeastern 

 North America, there is but one variety, the spores are all normal. 



M. J. Sirks (Bunnik). 



Jeffrey, E. C, Hybridism and the rate of evolution in 

 angiosperras. (American Naturalist. L. p 129—149. 1916.) 



Supporting his views, that hybridism is in general the cause 

 of pollen-sterility, the author brings in this paper following Statements: 



Epilobium \Charnaenerion) angustifolium in the northern part 

 of its American ränge, where it coincides with its allied species Epi- 

 lobium latifoHum, showed for the greater part of the individuals 

 (nine tenths) the pollen to be imperfect; in contrast, the materials 

 from the southern limits, where E. angustifolium does not coincide 

 in distribution with E. latifolium, are almost uniformly characterized 

 by a high degree of perfection. 



The monotypic species in the Onagraceae, Zauschneria califor- 

 nica, has pollen practically perfect, and the same State of affairs 

 is present in the two geographically limited species of Gongylocar- 



