356 OENOTHERA RUBRINERVIS, A HALF MUTANT. 



from above, the spikes show narrow, folded bracts in the first type 

 and flat, broad ones in the second type. This character is easily 

 appreciated and wholly reliable; no dubious cases trouble the coun- 

 ting in mixed cultures. The beginning of August, when the deserens 

 have opened only a few of their first flowers, is the best time to 

 separate them. A difference in the color has now become clear, the 

 red tinge of the parent type failing in the deserens. Here the leaves, 

 bracts, and flower buds are green, and the flowers are also of a purer 

 yellow. A number of smaller marks, which are helpful in the distinc- 

 tion, almost escape description, as, for example, the form of the 

 flowers, their grouping at the top of the spike, and the more erect 

 position of the buds before opening. 



The main character of 0. rubrinervis is the brittleness of all its 

 parts, as already mentioned. It is exactly the same in 0. deserens. 

 I have broken the stems of all the plants to be mentioned in this 

 article at the time of sorting them out in August or after harvesting 

 their seeds, but no exception has been found to this rule 1 ). Hybrids 

 which possess the other characters of rubrinervis, but lack the britt- 

 leness, are easily recognizable as rosettes of radical leaves as well 

 as during the growth of the stems. They will be designated as 

 subrobusta 2 ). 



The determination of the percentage of mutants in self-fertilized 

 seeds was made in 1916 in the following manner. The specimens 

 were counted in the boxes at the time of planting out in April and 

 the most undoubtful specimens of rubrinervis were counted and 

 destroyed. All the others were planted out and tried at the time 

 of flowering in August. By this means the space required for the 

 cultures was reduced to about one-half of what would have been 

 necessary if all the plants had been set out. Some losses were una- 

 voidable and the percentage figures may be a little too small in 

 ordinary cases. Only under favorable conditons do they come up 

 to the amount of the theoretical expectation, namely, one-third 

 of all the individuals. Since my question, however, was mainly to 

 decide whether all specimens of rubrinervis split into this form and 

 deserens, or whether there are also plants with a uniform progeny, 

 I shall give the figures as I found them. 



In the first place, I shall now describe the main line of 0. rubri- 



J ) I have, moreover, injected all the seeds for the sowings of the later years 

 under a pressure of 8 atmospheres during 48 hours, this being the only reliable 

 means of making the germination as complete as possible. 



2 ) Gruppenweise Artbildung, p. 143. 1913. 



