THE COEFFICIENT OF MUTATION IN OENOTHERA BIENNIS L. 13 



their progeny, to give constant and uniform strains and which 

 I have cultivated during a series of years under the names of 

 0. salicastrum and 0. salicifolia. 1 ) The first plants are as high as 

 0. biennis Chicago, attaining 2 and sometimes (1914) almost 3 

 meters in height. They differ mainly in having narrower leaves. 

 The salicifolia, on the contrary, is different from its parent species 

 in almost all respects, being richly branched and rarely attaining 

 one meter in height. It has almost linear leaves of a special blotted 

 green, small erect flowers and long thin fruits. Analogous muta- 

 tions have from time to time been observed in hybrid cultures of 

 0. biennis Chicago. 



Under the name of metaclinous hybrids I have described the 

 curious phenomenon that heterogamous species from time to time 

 produce among their hybrids from one cross, in one or a very few 

 specimens, the type which is ordinarily that of the reciprocal 

 hybrid. 2 ) For instance, the cross 0. biennis ChicagoxO. Lamarck- 

 iana gives the twin hybrids densa and laxa, while 0. Lamarckiana 

 xO. biennis Chicago produces the twins 0. laeta and 0. velutina. 

 Now among the first hybrid cultures sometimes a velutina, and 

 more rarely a laeta, arises, and among the latter sometimes a laxa. 

 Evidently some latent mutation, on the part of 0. biennis Chicago, 

 must be responsible for the production of these aberrant types. 

 Analogous metaclinous hybrids have been described for 0. atro- 

 virens Bartl. 3 ) 



Narrow-leaved mutations have also been seen in cultures of 

 0. muricata, and of late (1914) in those of 0. suaveolens Desf. 4 ) 

 Moreover, 0. gr audi flora, collected by Mr. Bartlett and myself 

 at Castleberry in Alabama, throws off aberrant forms, one of which 

 has broader and the other almost linear leaves. 5 ) 



i) For descriptions and figures see Gruppenweise Artbildung, pp. 304-307. 



2) Op. cit. p. 308. 



3) This is the species described in ray book Gruppenweise Artbil- 

 dung under the name of O. cruciata. For its metaclinous hybrids see 

 pp. 309—310. 



4) For the different varieties and mutations of O. muricata see also 

 Gates, R. R., A contribution to the knowledge of the mutating Oeno- 

 theras. Trans. Linn. Soc. II. Bot. 8:1 — 66, pis. 1 — 6, 1912. 



5) For O grandiflora see Gates, op. cit. p. ^- If the three types of 

 O. grandiflora, observed in my garden, occur also at Dixie Landing, 

 Alabama, and have crossed, each of them, with O. Tracyi, and have 

 perhaps produced twin hybrids and unlike reciprocals, this might 

 explain the large number of forms observed on that spot ; see Opera VI. 

 P- 552- 



