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IOWA ACADEMY OF SCIENCE Vor. XXIX, 1922 
ledge, we can see that they constitute a more or less correct non- 
scientific formulation of the truth. For example, the more or 
less rapid return of hybrids — that is to say, heterozygotes — to 
the parental forrps, is well established today as a fact of segrega- 
tion according to Mendelian ratios, which, if there is a single pair 
of allelomorphs in question, goes on, on a 1.2.1 basis in each 
successive generation. The more or less rapid return to its 
parents of the hybrid fertilized by parent is simply the splitting 
off of 50 per cent dominants or recessives as the case may be, and 
which are the parental types in the case of simple ratios. 
Wichura’s Work. — In 1865 there appeared Wichura’s memoir 
on the hybridization of plants, “Die Bastardbefruchtung im 
pflanzenreich, erlautert an den Bastarden der Weiden, Breslau, 
1865” based upon experiments in the crossing of willows, which 
had occupied him from 1852 to 1858 inclusive. A brief pre- 
liminary report had appeared in Flora in 1854, and also within 
the same year in the report of the Schlesische Gesellschaft. 
Taken as a whole, Wichura’s work dealt, not with the investiga- 
tions of individual specific characters but with species taken 
entire and crossed as such. As was the general custom, he re- 
garded a “species” as an integral whole that could be crossed in 
its entirety. With this exception he made what he called “binary,” 
“ternary” and “quaternary” crosses, i.e., crosses: (1) between 
two species; (2) between a species and a hybrid; and (3) crosses 
between two hybrids. Besides the smaller list of Wichura’s suc- 
cessful crosses, he published a much longer one of his failures, 
which stand as evidence both of the considerable amount of 
crossing work that was done and of the scientific integrity of the 
experimenter. Of the ordinary, or as he calls them, “binary” 
crosses, Wichura made, in all, thirty- five successful crosses and 
combinations of crosses (of which ten were “binary,” i.e., simple 
crosses in the ordinary sense) between twenty-one' different 
species of willows. 
Although, as has been stated, Wichura, no more than most of 
the other hybridists of his day, paid attention to the crossing of 
characters as such, he remarks upon the evidence of individual 
characters being inherited as such : “It was of interest,” he says, 
“to observe how the unusual narrowness of the leaves in the 
experiment, utilizing Salix purpurea x viminalis, remained still 
recognizable in the following generation ; a proof that, even in 
hybrid fertilization, individual characteristics of the parent plants 
can be inherited.” 
