igig] 



de vries—oeno thera r ubriner vis 



IS 



deductions from our formula. I have made quite a number of 

 further crosses between these two forms, partly in 1905 and partly 

 in 1913, using always the same family of rubrinervis, and taking the 

 combinations in both reciprocal directions. Six of them have given 

 for the third hybrid t>'pe rubrinervis and three of them subrobusta; 

 but since I have not determined the amount of lucida among them, 

 it is of no use to give the percentage figures. 



The exactness of the identification of the types in the formula 

 can be controlled by direct crosses with the constituents mut. 

 deserens and mut. velutina. The latter has been described under 

 the synonym O. blandina. I made the following combinations: 



The expectation for these crosses was: 



O. deserensXLamarckiana = 0. deserensX(typ.+velutina) = lucida+subrobusta 



O. blandina X rubrinervis = O. blandinaX (deserens4- velutina) = subrobusta+ velutina 



O. blandinaX deserens = 0. blandina X (deserens) = subrobusta 



Apart from the figure for lucida, which is too small, the results 

 of the experiments directly confirm the expectation. I have deter- 

 mined the amount of empty seeds for the four last named crosses, 

 and found almost none: 



Percentage of 

 Cross germs in seeds 



O. rubrinervis X blandina 97 



O. blandinaX rubrinervis 91 



O. deserens X blandina 100 



O. blandinaX deserens 90 



Moreover, I made the same determinations for the hybrids from 

 the two first named of these crosses, self -fertilizing them in 1916. 

 For the two latter crosses it was evident that the hybrids would 



