$35. BOTANICAL GAZETTE [NOVEMBER 
instance, therefore, affords a means for the experimental study of 
the origin of such a form by mutation. The main result of this 
study is the proof of the occurrence of mutant Mendelian hybrids 
besides the pure dwarfs. 
In my book on the mutation theory I have pointed out that the 
origin of O. brevistylis from O. Lamarckiana may have been induced 
by the mutation of a single sexual cell. If this combined in fertili- 
zation with a normal gamete, a hybrid would be produced which 
would not be distinct from the parent species in its external features. 
This hybrid would then, in its self-fertilized seeds, follow the law of 
MENDEL and produce, besides constant Lamarckiana plants, partly 
hybrids of the same type and partly specimens of the type of 
O. brevistylis. From this origin and the subsequent free intercross- 
ing in the field, the yearly appearance of O. brevistylis would receive 
a sufficient explanation (DEVRIES, op. cit., p. 506). 
If the process of mutation into this type were more often 
repeated, it should be possible to discover the original hybrids. 
They would, it is true, not be discernible from their normal sisters 
by external marks, but would yield, after artificial self-fertilization, 
about 25 per cent of brevistylis. And since mutants are produced 
ordinarily in a proportion of 1-2 per cent or less, the difference 
would be large enough to be noticed. Until now, however, such 
cases have not been observed. 
I have, therefore, been looking for another example in which a 
Mendelian behavior of the mutants might be associated with a 
normal coefficient of mutation from the parent species. Such 
cases would betray themselves by exceptionally high coefficients 
in single parent plants. Instances of such individual deviations 
are very rare, partly on account of the necessarily limited number 
of mother plants from which the seeds of our cultures are taken. 
But Scuouren’ has observed that Oenothera gigas, which ordinarily 
produces 1-2 per cent dwarfs, may be seen to throw them off in as 
large a number as 15 per cent. The same phenomenon has been 
described by Gates (op. cit., p. 137), who counted 9 per cent and 11 
per cent of dwarfs among the offspring of two self-fertilized plants 
of O. gigas. 
3 Schouten, A. R., Mutabiliteit en Variabiliteit. 1908. 
