420 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



The low fertility (only 9 were classed as fertile and 5 as partly 

 fertile) of the series Is noticeable and clearly shows that the ten- 

 dency of heterozygosity of interspecific rank is to give sterility. 

 Evidently the sterility is largely of the type I am classing as 

 Impotence, although this Is not certain, for at least one case 

 {Nicotiana Forgetiana X N. alata grandiflora) here reported fertile 

 is later (East '15a) reported as self-sterile (physiological incom- 

 patibility) but cross-fertile. Eight of the cases classed as fertile 

 are among hybrids that have Increased vigor. 



The evidence certainly fails to establish the point In question. 

 One can claim equally well that In the cases of increased vigor 

 and especially for those that are also fertile the results are due to a 

 similarity In respect to the cell organization of parent species 

 which admits of successful combination. 



V\\t\\ the Intervarietal crossing In tobacco the results are quite 

 as fluctuating and variable as are those of Darwin, and here the 

 writers are Inclined to consider, as Darwin did, that when such 

 intervarietal crosses show no Increased vigor it is not because of 

 simple relationship but because of similarity of gametic consti- 

 tution. As Burck has pointed out, the general application of 

 such a conception is untenable, and East and Hayes's results in 

 tobacco are fully as unconvincing as are the results reported by 

 Darwin. 



The most striking results were obtained In corn, in which as a 

 rule crossing between varieties Increases both vigor and seed 

 production over that of Inbred and self-fertilized stock. At first 

 glance the data seem most convincing and had such results been 

 obtained in tobacco the case would seem well established. How- 

 ever, It must be remembered that many races of corn are difficult 

 to self-fertilize on account of proterandry. Even with this 

 difficulty East and Hayes found that "decrease in vigor lessened 

 with inbreeding" and that "good and bad strains were Isolated" 

 (p. 22). Pedigreed line cultures, inbred, showed that no two 

 gave the same results; one strain of Leaming dent remained 

 vigorous and highly productive while another became nearly 

 sterile. Strains apparently similar in homozygosity show widest 

 variation indicative of spontaneous \ariation In natural vigor, 

 which is suggestl\-c that in such highly cullivatcd varieties as 

 corn extreme sporadic \ariations may be constantly occurring, a 



