No. 599] SHORTER ARTICLES AND DISCUSSION 



abortive or infertile all types of gametes or zygotes that may be 

 produced except the ones which carry forward the heterozygous 

 line. The test of a pure species is then not that it should breed 

 true (that is a corollary), but that it should produce gametes 

 uniform except as they may differ with respect to the factors 

 for sex characters. 



In laying such great stress on the phenomena of gametic and 

 zygotic sterility so very extensively present in the genus CEnothera 

 it must not be supposed that we have as yet established the de- 

 grees to which sterility may be genetic in its character or to what 

 extent it may be of a physiological nature. Only the sterility 

 that has as its cause the failure of the reduction divisions to 

 produce fertile gametes or the failure of the gametes to conjugate 

 freely can properly be of a genetic nature. There is probably 

 also a type of sterility due to physiological causes, as perhaps 

 malnutrition, and this might affect gametes and zygotes which 

 under favorable conditions would be fertile. We are very far 

 from an understanding of the causes of sterility in CEnothera, 

 to what extent cytological or to what degree physiological, and 

 it would at present be most unsafe to carry lines of speculation 

 very far in this field as regards the material under consideration. 



Professor De Vries has expressed strongly a belief in the 

 futility of my attempts to synthesize a Lamarckiana-like hybrid, 

 taking the stand that unless the parent stock is known to be 

 stable mutability might be inherited from one or both of the 

 parent species, or that variants, the result of a cross from impure 

 stock, might be mistaken for mutations. As a matter of fact 

 CEnothera biennis is known to be unstable, producing a small 

 series of "mutants," while 0. franciscana has not been tested for 

 its purity. Apparently Professor De Vries and I are working 

 from assumptions that are far apart. The inheritance of a 

 mutating habit such as that claimed for Lamarckiana would 

 mean to me the inheriting of a heterozygous germ plasm running 

 back to some hybrid origin. To me phenomena such as is ex- 

 hibited by Lamarckiana in throwing its "mutants" indicates in 

 itself the probability of heterozygous germ plasm. If this be- 

 havior is to be presented as evidence of mutation the purity of 

 Lamarckiana must be established beyond all reasonable doubt 

 and this in my opinion has not been shown. The tests of cross 

 breeding, when twin hybrids result, and the very high degrees 

 of gametic and zygotic sterility strongly indicate genetic im- 



