330 PLANT HYBRIDIZATION BEFORE MENDEL 



The mean for all the experiments is given as 24.93 per cent. 



De Vries adds further : 



"The experiments comprise ordinarily a few hundred, sometimes about 

 1,000 individuals. With many other species I obtained corresponding re- 

 sults." (la, p. 87.) 



The analysis of the 75 per cent apparently dominant follows : 



"The distinguishing of the remaining 75% in the two groups cited is 

 much more troublesome. It requires that a number of individuals with 

 the dominating character be fertilized with their own pollen, and that, 

 in the next year, for every plant, the progeny be cultivated and counted. 

 This was carried out in 1896 for Papaver somniferuin (Mephisto) X Dane- 

 brog. From the first generation of 1895, the progeny of the succeeding 

 year were found to be as follows : 



Dominating (Mephisto) 24% 



Hybrids (with 25% Danebrog) 51% 

 Recessive (Danebrog) 25%" {ib., p. 87.) 



De Vries states {ib.^ p. 88.) : 



"This result corresponds to the above assumed formula. Or, more cor- 

 rectly, out of these figures I first derived the formula. 



"The dominating and the recessive characters show themselves accord- 

 ingly constant in the progeny, as far as they were isolated through 

 segregation. The hybrids, however, split again according to the same law. 

 Thty furnished, in this experiment, on the average, 77% with the domi- 

 nating, and 23% with the recessive character. 



"This behavior remains, in the course of the years, the same. I have 

 continued this experiment through two still further generations. The 

 50% hybrids split ; the 25% dominating remain constant." {ib., p. 88.) 



De Vries also confirms the principle that the hybrid, crossed 

 with either of the two parents, gives the progeny which, for the 

 character in question, are 50 per cent : 50 per cent. The cases are : 



% Year 

 Clarkia pulchella X white 50 1896 



Oenothera lamarkiana X brevistylis 55 1895 



Silene armeria {red) X white 50 1895 



Crosses were also made (1897), between the prickly Datura 

 tatula and the smooth D. stramonium inermis. The plants of the 

 first generation were blue with prickly fruits, as follows : 



Flowers % 



blue (dom. -f- hybrid) 72 



white (recessive) 28 



Fruits % 



Smooth blue 26.8 



Smooth white 28.0 



Av. 27.4 {ib., p. 89.) 



