12 



THE AMERICAN NATURALIST 



[Vol. LV 



or less homogeneous substance ; and in so far as numer- 

 ical and geometrical order is exhibited by them, it would, 

 in my opinion, be more proper to compare this regular- 

 ity with that seen, for example, in drying mud or in the 

 formation of prisms of basalt, than to attribute to it a 

 more fundamental meaning. 



Lea^dng these speculative considerations, and limiting 

 our inquirj" to the concrete question, at what moment in 

 the cycle does genetic segregation occur, we reach a per- 

 fectly definite answer: that whatever future research 

 may decide as to the occurrence of segregation in ani- 

 mals—which, for aught we know, may always be effected 

 at the reduction division — there is no such limitation in 

 plants. We are now thoroughly familiar with a large 

 group of examples in which the genetic properties of the 

 male and female cells of the same plant are quite differ- 

 ent. In these, at all events, the reduction-division can 

 not be the moment of the segregation by which these 

 characters are distributed. 



The first case detected was in Matthiola, where Miss 

 Saunders' results proved that in the double-throwing 

 singles the pollen carries exclusively doubleness, the eggs 

 being mixed, some single and some double. A similar 

 condition was shown to exist in regard to the cream and 

 white plastids, respectively, the pollen grains bearing ex- 

 clusively cream. De Vries observed a comparable ar- 

 rangement among the CEnotheras, and Eenner has lately 

 shown that the phenomenon is widely spread in that 

 group, thereby providing a consistent interpretation of 

 much that was formerly obscure in the genetic behavior 

 of these plants. In Campanula carpatica Miss Pellew 

 proved that the pollen grains of the hermaphrodite form 

 called pelvifonnis carry exclusively femaleness, and 

 preponderantly white flower-color (the plant being 

 heterozygous for blue). The case of Petunia investi- 

 gated by Miss Saunders® is somewhat peculiar in 

 the fact that in the heterozygous singles the male side 

 carries the dominant singleness only, since in those in- 



sjour. Gen., Vol. 1, p. 57 (1910). 



