i9i6] DeVRIES— DIMORPHIC MUTANTS 257 



the percentage figures come so much nearer to equality of the two 

 types than in the other cases is probably owing to this striking vigor 

 of the race. The means are 25 per cent cana for no. i and no. 2, but 

 53 per cent cana for no. 3. The proportion of mutants among the 

 seedlings of the cana individuals is 18 in 350, or about 5 per cent. 



O. cana from lata nos. 4 and 5. — ^As previously mentioned, the 

 progeny of two further mutants of the same origin have been 

 studied. The offspring of one of them embraced only 15 indi- 

 viduals, of which 13 have flowered. There were 3 cana, 2 mutants 

 (one oblonga and one of the same new type as in no. 2), the 10 

 remaining plants being externally like 0. Lamarckiana. The 

 second original mutant yielded only 11 offspring, among which 

 7 were cana, one Lamarckiana, and 3 oblonga. Although these cul- 

 tures do not justify the calculation of percentage figures, they 

 evidently support the conclusions drawn from the three former 

 ones, and argue for the conception that this form of splitting is 

 typical for 0. cana. 



Intluence of culttjre on percentage figures. — I have 

 shown' that the percentage figures for the splitting of 0. scintillans 

 in the succeeding generations may differ for different families. 

 Sometimes it is only 15 per cent, more often it varies between 34 

 and 39 per cent, and in rare cases it reaches 69-93 P^r cent. Sub- 

 sequent experiences have suggested the idea that these differences 

 are due mainly to outward conditions or to the method of cultivation, 

 and that favorable influences must increase the percentage of indi- 

 viduals with the type of scintillans a,n.d diminish the percentage of 

 Lamarckiana-]ike specimens. 



The self-fertilized seeds of the cana individuals previously 

 mentioned have given the following percentages of specimens 

 with the cana type: 15 and 16 per cent, 24-34 and 35 per cent, and 

 46 and 60 per cent, the two latter being found in a culture which 

 excelled the others in vigor. Evidently these figures run parallel 

 to those of scintillans and the variability must have the same cause 

 in both cases. 



In order to ascertain the nature of this cause I have tried to 

 answer two questions, namely: (i) are the percentage figures 



' The mutation theory. Chicago. 1909. pp. 388-391. 



