176 OENOTHERA LAMARCKIANA MUT. VELUTINA. 



ment at a much later stage. The proportion of these can be diminished 

 by a better culture, and therefore they may be considered as a 

 result of the crowding of the seeds in the capsules, combined with 

 the limited amount of nourishment available for them. 



Our new mutant velutina produces hardly any abortive seeds, 

 at least under normal conditions of culture. I tried the seeds from 

 purely pollinated capsules of 4 specimens of my culture of 1915, 

 which was the fourth generation of my race. I took them carefully 

 out of the fruits, mixed those of 5 successive capsules of the same 

 spike, and counted 200 grains from each lot. I soaked them in water, 

 pushed this into their seed coats by means of a pressure of 8 at- 

 mospheres for about 24 hours, and afterward laid them out to 

 germinate in small glass tubes in a stove at 30° C. 1 ). Within 6 days 

 the larger part of the seeds germinated, giving percentages of 85, 

 84, 73, and 70 for the 4 lots. I then opened the remaining grains 

 and found fully developed germs in almost all of them. The percent- 

 age of germs, being the sum of the two trials, came to 99, 96, 96, 

 and 93, and there is no doubt that if they had been left in the stove 

 for a longer time, almost all of the resting germs would have shown 

 signs of germination. 



The proportion of rapidly germinating grains and that of empty 

 ones depend in a high measure upon the external conditions of life. 

 During the summer of 1914 I cultivated 2 lots of individuals from 

 seeds of the same parent plant, giving to one of them the ordinary 

 favorable conditions of my garden, and keeping the others in a dry 

 soil without manure. The seeds of the 2 most vigorous specimens 

 of both lots, taken from self-fertilized capsules, were tried. They 

 contained 99 and 99 per cent of germs for one group, but only 

 72.5 and 73.5 per cent for the other group. The same effect was 

 shown in the amount of grains which germinated within the first 

 6 days. The figures were 80—88 per cent in one case and 53 percent 

 in the other case 2 ). 



The loss of the hereditary property of producing about 50 per 

 cent of empty grains constitutes a latent mutation accompanying 



x ) This method has been followed in all the experiments to be described in 

 the text. It is described in the following papers: The coefficient of mutation 

 in Oenothera biennis L. Bot. Gaz. 59: 190—194. 1915. Opera VII, p. 1. and 

 in : Ueber kiinstliche Beschleunigung der Wasseraufnahme in Samen durch 

 Druck. Biol. Centralbl. 35: 161-176. 1915. Opera VII, p. 56. 



2 ) Biol. Centralbl. 35: 174-175, Opera VII, p. 70, where O. blandina was 

 provisionally indicated as mut. nov. B. 



