198 Varietäten, Descendenz, Hybriden. 



effect. One hypothesis appears to meet the case. If all the grandi- 

 flora chromosomes are equally effective in inhibiting anthocyanin 

 production in the hybrids with ruhricalyx, then the dilution effect 

 will be the same in F^ or in crossing back, whenever an R chro- 

 mosome is present in the next generation. It would thus appear to 

 be unnecessary to assume that this chromosome is itself modified 

 by its different nuclear and cytoplasmic environment. There can be 

 no question that the R character is permanently diluted by crossing 

 with grandiflora, and the degree of dilution is increased every 

 time the hybrid is again crossed back with that species. 



Another noteworthy fact is that as the pigmentation becomes 

 more dilute its morphological expression is more irregulär. Instead 

 of a continuous pigmentation of the whole bud a patchy effect will 

 be produced. To account for this condition through the accession 

 of a "Spotting factor" is a gratuitous assumption. 



M. J. Sirks (Bunnik). 



Jeffrey, E. C, Some fundamental morphological objec- 

 tions to the mutation theory of De Vries. (American Na- 

 turalist. IL. p. 1—21. 1915.) 



Cytological researches were made by the writer on pollen- 

 development in some species of Onagraceae, f. i. Fuchsia speciosa 

 hybr., Epilobiurn angnstifolinni , E. hirsutmn, Oenothera biennis and 

 O. Lainnrckiana. 



The multiform gardenhybrid Fuchsia speciosa showed more 

 than a third of the pollen present in its anther cavities as abortive; 

 the very constant and invariable Epilobiurn angitstifolium, someti- 

 mes referred to a separate genus as Chamaenerion augustifoliiini, 

 forms is pollengrains not in tetrads but separate and very uniform 

 and perfect in its development without signs of degeneration, while 

 E. hirsuttim, a species of the ordinary Epilobiurn type and hybrid 

 in a very high degree, contained a great many abortive pollengrains 

 in its anthercavities. The species of the genus Oenothera, examined 

 by the writer, a. o. 0. biennis and O. Laniarckiana have shown in 

 every instance a greater or smaller amount of abortive pollen as a 

 characteristic feature of the anther contents. 



From a comparison of the conditions of sporogeny found among 

 the lower plants, the Brj'-ophj^ta, the Pteridophyta and the G3^mno- 

 sperms, the general conclusion can be drawn that hybridism is 

 rare among them and that where it occurs it is accompanied by 

 the phenomenon of spore abortion; among the Angiosperms with 

 their nearly one hundred and fifty thousand recognised species, 

 hybridism is very commonly recognized and always in a more or 

 less connected way with abortion of pollengrains. 



The writer's own conclusions, drawn from his researches, run 

 as follows. 



1. The Onagraceae are largely characterized by hybrid conta- 

 mination in nature. 



2. This Statement holds with particular force for Oenothera La- 

 marckiana and other species of the genus Oenothera , which have 

 served as the most important basis of the mutation hypothesis of 

 De Vries. 



3. Constant hybrids or crypthybrids are of verj^ common occur- 

 rence among the Angiosperms and have been illustrated in the pre- 

 sent article by reference to the genetical conditions occurring in 

 certain Rosaceae. 



