172 OENOTHERA LAMARCKIANA MUT. VELUTINA. 



67 per cent velutina and 33 per cent laeta. Why the large-flowered 

 laeta should split, but the small-flowered type remain constant, 

 is a question which will have to be studied later. 



0. blandina laeta has been, throughout its whole evolution, exactly 

 the same type in the 3 crosses already mentioned, and whose progeny 

 I cultivated in both years side by side. In the seed pans and the 

 transplanting boxes the young plants are almost exactly like 0. 

 Lamarckiana, resembling this form far more than any of the hybrid 

 laeta do. This condition prevails until the beginning of flowering, 

 during which period the leaves of the stem are somewhat broader 

 and less covered with bubbles than in the parent species. This 

 difference is then seen to increase gradually and becomes evident 

 in the lower bracts of the inflorescence, which are broad, especially 

 at their base, smooth, and wholly or almost without bubbles. As 

 the spike develops, the difference from the parental type becomes 

 greater. The fruits are less crowded and somewhat stouter, and the 

 plants gradually reach a greater height than specimens of 0. Lamarck- 

 iana planted at the same time and under the same conditions. 

 Although the differences are still small, apart from the smoothness 

 of the leaves, the plants of 0. blandina laeta cannot be mistaken 

 for Lamarckiana during all the time of flowering, which may last 

 more than 2 months. 



It seems probable that the increased breadth and the diminished 

 bubbles of the higher leaves of the stem and of the bracts of the 

 inflorescence are expressions of a single change, which must consist 

 in a thorough stretching of the blade parallel to its surface. If this 

 be so, we may conclude that the bubbles, which are so characteristic 

 of 0. Lamarckiana, are due to some deficiency in this stretching 

 and thereby constitute a recessive character. If this conclusion be 

 granted, the smoothness of the leaves of 0. blandina must be dominant 

 in its crosses with 0. Lamarckiana, and in this way be transferred 

 to both of its twins, causing the one to be a laeta instead of a pure 

 Lamarckiana. We are thereby provided with a beginning of an ex- 

 perimental analysis of the marks of mut. velutina, as already discussed. 



Here I might insert some considerations concerning the mutative 

 origin of 0. blandina. We have seen that 0. Lamarckiana and 0. 

 nanella, when crossed with this new form, repeat its characters in 

 part of the offspring. In the same way a mutant velutina may be 

 produced by the conjugation of a mutated sexual cell with a normal 

 one. Thus it is not necessary to assume the accidental meeting 

 of two mutated gametes, which would obviously make the chance 



