210 MASS MUTATIONS AND TWIN HYBRIDS OF 



close. All those species which split 0. Lamarckiana into the twins 

 laeta and velutina provoke the same phenomenon in 0. grandiflora. 

 Moreover, 0. biennis Chicago, when used as a female parent in the 

 crosses, splits both of them into laxa and densa. In their characters 

 the twins of both species resemble each other so closely as to be 

 easily identified, although it is evident that they cannot agree in 

 all their characters. In those of 0. grandiflora the differentiating 

 marks are not so sharp as in the twins of 0. Lamarckiana, and it 

 is sometimes difficult to recognize them in the first culture which 

 offers them. As soon as a second generation is grown, however, 

 all doubts disappear. 



The species which split 0. Lamarckiana into laeta and velutina 

 are 0. biennis, 0. syrticola (muricata), and 0. suaveolens when used 

 as female parents; 0. biennis Chicago, when its pollen is used; and 

 0. Cockerelli in both reciprocal crosses. 0. biennis Chicago fecun- 

 dated by 0. Lamarckiana produces the twins laxa and densa. All 

 these instances are duplicated by the analogous crosses of 0. gran- 

 diflora. Moreover, 0. Hookeri produces twins in the reciprocal 

 crosses with 0. Lamarckiana and also with 0. grandiflora, but the 

 results of these crosses are of a more complicated nature, and there- 

 fore will not be dealt with in this article. Table III gives a list of 

 my crosses, together with their main results. 



In 0. suaveolens x grandiflora 18 per cent of yellow specimens 

 appeared; in the other crosses, however, only the twins mentioned 

 appeared. If we sum up the figures for laeta and velutina and take 

 their mean, we find 52 per cent laeta and 46 per cent velutina, show- 

 ing that the figures do not deviate essentially from equality for the 

 two groups. Mutants were rare in these cultures. Among Vat' laeta 

 of the first cross an ochracea and a lorea were seen, and among its 

 velutina a sulfurea. Moreover, a lorea appeared in the second ge- 

 neration of the laeta of 0. lorea x Cockerelli. The table proves the 

 complete analogy between the splitting phenomena of 0. grandi- 

 flora and 0. Lamarckiana. 



0. biennis x grandiflora. — I made this cross in 1914 and culti- 

 vated the first generation in 1915. It embraced 60 plants, almost 

 all of which flowered in July and August. In the beginning of the 

 flowering period I noticed the presence of two distinct types. The 

 uppermost leaf beneath the spike was broad in laeta (3 x 10 cm.) 

 and narrow in velutina (2x7 cm.), as were also the leaves and 

 bracts. The color was yellowish and pale in the first, but less so in the 

 second type. The velutina began to flower about a week after the 



