194 BOTANICAL GAZETTE [march 



A sample of seeds of 0. biennis, taken from a late flowering 

 individual, produced only 2 per cent of seedUngs in the first two 

 days, while a control sample, after having been exposed in water 

 to a pressure of 6 atmospheres, produced at once 80 per cent of 

 seedlings. In the same way for 0. suaveolens, the percentage was 

 increased from 3 to 14 per cent, for O. muricata from 12 to 80 per 

 cent, and for O. Cockerelli, a species which is often very slow in 

 germinating, from 2 to 72 per cent. 



It is not improbable that in 0. Lamarckiana the hard seeds 

 may contain more mutants than the easily germinating ones, which 

 have thus far been studied. It seems even possible that they may 

 conceal some new, as yet unobserved, types of mutations. The 

 new method enables us to bring almost all the germs to germination, 

 as well as to separate the seedlings of the different groups. 



Before concluding, I may be allowed to recommend this method 

 for the study of various other kinds of seeds, also. 



Summary 



1. In a culture of 8500 specimens of pure line Oenothera biennis 

 L., 8 mut. nanella, 4 mut. semigigas, and 27 mut. sulfurea arose, 

 giving the percentages of about o . i per cent, o . 05 per cent, and 

 0.3 per cent. In cultures of 0. Lamarckiana the corresponding 

 numbers are for 0. nanella 1-2 per cent, for 0. semigigas o . 3 per cent 

 (Gruppenweise Artbildung. p. 329), while no color mutations have 

 been observed as yet. With the origin of 0. Lamarckiana the 

 mutability for dwarfs, therefore, must have increased at least 

 tenfold, and for gigas types about sixfold. The material cause 

 for this improvement is in all probability the same as or closely 

 connected with the cause of the largely increased number of 

 mutative forms which are known to start from O. Lamarckiana. 



2. From the cross O. biennis mut. nanellay.0. biennis only 

 dwarfs of a uniform type arose (108 Ex). O. biennisXO. biennis 

 mut. nanella was in the first generation exactly like pure biennis; 

 0. LamarckianaXO. biennis mut. nanella exactly like O. Lamarckiana 

 y. biennis. 



O. biennis semigigas is self-sterile, but when pollinated by 

 0. biennis gives for one-half pure biennis with 14 chromosomes, and 

 for the other half a new, slender type with 15 chromosomes. 



