GENOTHERA AND THE MUTATION THEORY 311 
supposed to account for the types named, such 
differences do not offer an explanation of most of 
the other new types nor of the peculiar behavior 
shown by species crosses in the genus CEnothera. 
As will appear below these two classes of phenomena 
both suggest strongly that the plants are heter- 
ozygous, in spite of the fact that they breed nearly 
true. 
If O. biennis and O. syrticola (muricata) are 
crossed, the F; hybrid strongly resembles the male 
parent, whichever way the cross is made. Com- 
binations of these hybrids with each other and with 
both parent species have shown that the pollen 
and egg cells of each species carry different genes. 
The chief characteristics in which the two species 
differ are transmitted only through the pollen, and 
only the minor differences between the hybrids and 
their respective fathers are due to genes transmitted 
by the eggs... The hybrids themselves behave in 
the same way so far as these characteristics are 
concerned; what they received from their father 
they transmit only through their pollen, what they 
received from their mother they transmit only 
through their eggs. As was pointed out by deVries, 
this phenomenon is perhaps to be connected with 
the fact, discovered in 1901 by Geerts, that about 
half the pollen grains and about half the ovules 
degenerate in certain of the @inotheras—apparently 
1 These two species are quite similar, so that the characters transmitted 
in this peculiar fashion constitute only a small proportion of all the 
characters of the plants. 
