Oenothera Leptocarpa. 355 



origin of two examples of this species will be found 

 recorded in the pedigree of a branch of the Lamar ckiana- 

 family which appears on page 262. It occurred in a 

 culture of about 10,000 seedlings in 1895, of which 

 about a thousand flowered. This indicates a frequency 

 of about 0.2 %. I have noted the appearance of single 

 individuals both before and after this, but have not the 

 data from which to calculate the frequency of their oc- 

 currence. 



0. leptocarpa has arisen from O. riihrinervis, as well 

 as from 0. Lamar ckiana, but not from any other new 

 species. After I had become familiar with this fact 

 I found them fairly frequently. A character peculiar to 

 0. leptocarpa is that it flowers very late — a character 

 which has greatly diminished the prospect of discovering 

 the species. For as soon as the plants on a bed begin 

 to flower, seed-parents are chosen for self-fertilization. 

 And I generally remove a certain number of the plants 

 surrounding these either to allow them to grow more 

 freely or to have plenty of room for my operations. This 

 involves the destruction of the weaker plants with which 

 the late flowering leptocarpa are easily confused. 



The riihrinervis cultures were usually made with a 

 rather special end in view and therefore consisted of no 

 more plants than were wanted as seed parents. The 

 plants were grown for example for the purpose of mak- 

 ing certain crosses which I had decided upon or for the 

 experiments with tricotyly which I have already men- 

 tioned, and in these latter of course selection took place 

 directly the seed came up. So that the proportion in 

 which leptocarpa appears in such cultures is no indica- 

 tion at all of what the mutation-coefficient of that species 

 really is. 



