1 88 Ikeno . — On Hybridization of some Species of Salix. II. 
development only by its stimulating action (pseudogamy). As before 
stated, I have observed frequently in catkins covered with bags ovaries 
which have grown up somewhat more intensely than others and yet remain 
quite sterile ; may not such ovaries be able to produce some seeds 
by the stimulus of foreign pollen ? This is, however, a mere supposition, 
and the fact ought to be studied in future more in detail, because it is 
quite possible that exceptionally a much larger number of ovules than 
I was able to observe in my experiments might develop to seeds without 
any pollination. 
The results of experiments of Pellew and Durham with Primula 
verticillata, floribunda , and the hybrid between them, P. Kewensis y l agree 
in several respects with what I have seen in our Salix. It appears that 
they have also met with autonomous as well as induced parthenogenesis, for 
they say , 2 ‘ We incline to suppose that the ovules are such that while they 
can occasionally develop without fertilization they more commonly develop 
in consequence of that stimulus.’ 
Concerning the above experiments of Pellew and Durham, Winkler 
makes the following remarks, which are reproduced below in his own words : 
‘ Vor Allem aber ist . . . zu bedenken, dass die apomiktische Samenbildung 
auch ohne jeden Bestaubungsreiz erfolgen kann, so dass ein solcher als 
Auslosung der vermuteten Parthenogenesis jedenfalls nicht unentbehrlich 
sein, sondern hochstens fordernd wirken kann. Dann kann man aber auch 
nicht von einer durch die Bestaubung induzierten Parthenogenesis spre- 
chen . . . sondern nur davon, dass durch den Pollenschlauchreiz die an 
sich schon vorhandene Neigung zur apomiktischen Samenbildung gefor- 
dert wird. . . .’ 3 All that Winkler says may be true, and also applicable to 
our case of Salix . To decide, however, experimentally the fact whether 
pollination has induced parthenogenesis, or has simply accelerated (‘ for- 
dern ’) the tendency for apomictic development, would not be easy. 
Had we to deal in our case with parthenogenesis, either autonomous 
or induced, the following remark might not be without some interest. It 
is clear that parthenogenesis has been originally derived from normal 
fertilization in the course of phylogenetic evolution. In respect to the 
manner of its origin there may be two possible ways. Firstly, certain 
animal or plant forms which have reproduced themselves at first by normal 
fertilization acquire at once the power of complete parthenogenesis by 
mutation, so that all eggs or ovules reach suddenly a condition such 
that they need no fertilization for their further development. Secondly, 
the transition from fertilization to parthenogenesis is gradual, i. e. several 
stages intervene between the two extremes — as we see, for instance, in some 
1 Journ. of Genetics, vol. v, 1916, pp. 159-82. 
2 1. c., p. 160. 
3 Ursache und Verbreitung der Parthenogenesis im Pflanzen- und Tierreich, Jena, 1920, p. 175. 
