28 OENOTHERA GIGAS NANELLA, A MENDELIAN MUTANT. 



Mendel and produce, besides constant Lamarckiana plants, partly 

 hybrids of the same type and partly specimens of the type of 0. 

 brevistylis. From this origin and the subsequent free intercross- 

 ing in the field, the yearly appearance of 0. brevistylis would receive 

 a sufficient explanation (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 nor- 

 mal 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 

 Schouten 1 ) 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 0. gigas. 



From time to time I have noticed the same deviating percent- 

 ages in my own cultures. Thus, for instance, I fertilized in 1910 a 

 specimen of 0. gigas by its own pollen, and among 50 seedlings of 

 its offspring 10 were dwarfs, pointing to a percentage of about 20 

 per cent 2 ). Similar facts have since occurred more than once in my 

 cultures. 



Schouten and Gates have interpreted these figures as indicating 

 a Mendelian proportion of dwarfs, and on this assumption the 

 parent plant would have been a mutant hybrid in the same sense 

 as explained above for 0. brevistylis. Mutant hybrids would then 

 occur in a race which produces dwarf mutants also, and the latter 

 would then, of course, have to be considered as the products of the 



i) Schouten, A. R., Mutabiliteit en Variabiliteit. 1908. 

 2) Gruppenweise Artbildung, p. 340, 19 13. 



