No. 509] T11F ( . 1 TFdORIFS OF VARIATION 



L>71 



theory would be destroyed. This is a question upon 

 which we are sadly in need of light. Some of De Vries's 

 own mutations are, however, quite inconstant and show 

 a. strong tendency to revert to the parent species. 

 (Enothera scintillans, when self -pollinated, produced from 

 8 per cent, to 52.9 per cent, of Lamar ckian as and .'U per 

 cent, to 69 per cent, of its own kind and a variable number 

 of other mutants. 0. elliptica and 0. linearis repeat their 

 kind in still smaller ratios. The reversion of these 

 mutants like their origin is sudden, but it shows an un- 

 stable condition of their germ plasm and it may be ques- 

 tioned if this reversion is essentially different from the 

 slower reversion which often follows the cessation of the 

 selection of ordinary fluctuations. 



That the differences between mutations and fluctua- 

 tions are not so fundamental as the pangen theory implies 

 is indicated by several facts, some of the most suggestive 

 of which have been furnished by De Vries's own experi- 

 ments. For a number of years De Vries carried on a 

 series of experiments on the corn-marigold Chrysan- 

 themum segetum, with the purpose of creating a double- 

 flowered variety. De Vries chose a garden variety of 

 this form, grandiflorum, and raised several generations, 

 selecting the seed each time from heads which contained 

 13 rays florets. After four years of propagation, when 

 he was satisfied of the purity of the isolated strain, De 

 Vries began to discard all plants with less than HI rays 

 in the terminal head. The selection was continued for 

 a number of generations when a plant appeared which 

 seemed to form a promising one for the production ot a 

 double variety. 



It was not remarkable for its terminal bead, which exhibited the 

 avera,, number of rays of the 21-rayed race. Nor was it d t g si e 1 

 by the average figure for all the heads. It was only selected because 

 it was the one plant which had some secondary heads with one ray m 

 than all the others. This indication was very slight and «oM not 

 have been detected save by the counting of the rays of 

 heads. But the rarity of the anomaly was exactly the indica ion 

 wanted, and the same deviation would have had no significance what- 



