202 MASS MUTATIONS AND TWIN HYBRIDS OF 



hypotheses superfluous 1 ), but this point must be reserved for another 

 article. 



I shall first describe my cultures and crosses of 0. grandiflora in 

 a purely empirical way and afterward discuss their results in con- 

 nection with those of Bartlett. 



A. Mutations of 0. grandiflora. 



One of the last days of September 1912 I visted with Bartlett 

 a station of 0. grandiflora in the neighborhood of Castleberry, Ala- 

 bama. It was on the border of a cornfield situated along the rail- 

 road. The station seemed to us to be pure, since no other species 

 of the same group could be discovered either in the field itself or in 

 its neighborhood. The number of specimens was small, but had 

 been very large some years ago, when the field was not cultivated. 

 A few specimens bore ripe capsules, which we collected. From 

 their seeds I started 10 pure strains. One of them was continued 

 through four succeeding generations (1913—1916), whereas the 

 others were abandoned as soon as they proved to contain in the 

 main the same derivatives. 



This race produced in my garden three mutations, two of which 

 were observed in every generation, but the third was very rare, 

 occurring only once 2 ). All of them were constant in their progeny. 

 I shall call them ochracea, characterized by broad and pale leaves, 

 mostly weak and of a low stature (fig. 1); lorea, with almost linear 

 leaves and somewhat narrower petals (fig. 2); and gigas, with stout 

 stems, broad leaves and flower buds, large flowers, and 28 chromo- 

 somes in its nuclei. As was to be expected, besides this gigas there 

 was also found a semigigas, but since it was wholly sterile, little 

 weight can be attached to it. Gates (10) observed a dwarf mutant 

 of 0. grandiflora, but no dwarf occurred among my cultures. 



The pedigree of the whole culture is as follows. All fecundations 

 were pure self-fertilizations, made by myself. 



*) See Gruppenweise Artbildung. The conception of Renner that the twins, 

 and with them all mutability, might be the effect of a hypothetical hybrid condition 

 of O. Lamarckiana, runs in some respects parallel to this vieu, but is contradicted 

 by it on its main points. See Zeitschr. Ind. Abst. und Vererbungsl. 16: 279—284. 

 1916. 



2 ) All of the seeds for the different cultures were soaked in water under a 

 pressure of 8 atmospheres during about 48 hours, and then sown at 30° C. in 

 the greenhouse, so as to induce the most complete germination. 



