Oenothera Ohlonga. ZZ7 



nevertheless, found it on perfectly healthy annual plants 

 whose main stems have been heavily laden with fruit. 



I have already recorded experiments on the con- 

 stancy of O. rtihrinervis § 3 (p. 232) and § 5 (p. 274). 

 These experiments show that plants raised from the seed 

 of mutated individuals are exactly like their parents, and 

 that the characters we have described for the parents 

 reappear in the children in exactly the same degree. O. 

 ruhrinervis itself is very slightly mutable and seems to 

 confine itself to throwing off lata and leptocarpa, as al- 

 ready shown on page 273. 



§ 14. OENOTHERA OBLONGA. 

 (Plate VI.) 



0. ohlonga has arisen much more frequently than 

 O. rnbrinerz'is both from 0. Laniarckiana itself and 

 other species and crosses. I have seen it arise altogether 

 about 700 times from one form or another of known 

 and pure ancestry. The various cultures in which it 

 arose comprised about 70,000 seedlings. We might 

 therefore almost speak of coefficients of mutation ; which 

 in the case of this species would be about 1 '^/c, in the 

 case of O. ruhrinervis 0.1 % and in that of 0. gigas 

 0.01 %. 



What is the cause of these differences? They cannot 

 be ascribed to defective observation. I first saw 0. oh- 

 longa in 1895 when my cultures were very extensive; in 

 previous years they were probably there, but escaped my 

 observation. Their young rosettes are as easy to recog- 

 nize as those of O ruhrinervis; and often somewhat 

 earlier, as rosettes with six leaves. But evidently this 



