28o Ostenfeld. 



of the Hieracia and the pure-breeding of the hybrids. Together with 

 this case he puts forward the remarkable fact that in certain Orchids 

 a species, when fertiUzed with the pollen of different other species, 

 still gives rise to an offspring which is completley like itself and shows 

 no trace of the father parent. He considers this phenomenon, which 

 he calls monolepsis, as "tantamount — as regards hereditj? — to 

 parthenogenesis" (1. c. p. 249). 



With regard to the sexual types (B) almost all the known cases are, 

 in Bateson's opinion, "open to the criticism made in the last section, 

 that either actual parthenogenesis or monolepsis may be occurring" 

 (p. 249), as far as the question is about plants. He quotes as the most 

 trustworthy cases DE VrieS's above mentioned Oenothera rmiricata x 

 biennis and JA^■CZE\VSK^s Anemone silvestris x magellanica; but both 

 these cases have in common that the fertility in the hybrid is very 

 limited, which fact Bateson expressly mentions as weakening the 

 convincing power of the cases. The same objection is made more 

 emphatically by R. H. Lock (1909) who says that such cases do not 

 prove anything, for perhaps the segregating factor is hidden in such 

 a way that those germ-cells which should give the segregating in- 

 dividuals, are not functional. This objection is, in my opinion, valid. 

 If then the vegetable kingdom does not show any incontestable case 

 of true-breeding hybrids i), still some, though few, are found within 

 the animal kingdom (mulatto, rabbits, butterflies), so that the existence 

 of true cross-breeding cannot be denied, but we must clearly under- 

 stand that it is the exception, and segregation the rule. 



Even if B.\teson's position is rather extreme, I think that this 

 reaction is useful, especially as it makes clear to us what we know 

 with certainty in this matter, — and that is very little, at least with 

 regard to species hybrids. 



In W. JOH.\NNSEN's "Elemente der exakten Erblichkeitslehre" 

 (1909). published a few weeks before Bateson's book, similar points 

 of view are held out. Johannsen defines clearly and appropriately 

 constant hybrids thus: "darunter versteht man ein Kreuzungsprodukt, 

 Fj, das nicht spaltet" (p. 424), and also for him they are the ex- 

 ception, segregation the rule. In contradiction to DE VRIES, he — as 



') Bateson does not seem to know a paper (written in Swedish) by T. Hedlund 

 (1907), according to which a Malva hybrid (M. parviflora x oxytoba) seems to be 

 quite fertile and constant in its offspring and still to have full fertility, but the 

 experimental method of Hedlund is perhaps not quite indisputable. 



