No. 642] 



VARIATION IN DATURA 



27 



fulfilled and we have obtained, in the offspring of a tri- 

 ploid, practically the full range of (2m + 1) mutants as 

 well as double mutants of the formula (27? + 1 + 1). Xo 

 modified triploids have as yet been identified, but even if 

 we found them we could not expect to be able to propa- 

 gate them by seed. 



Heterozygous tetraploid plants also show curious 

 ratios, according to whether there are 1, 2, or 3 doses of 

 the dominant factor. Duplex plants give a 35: 1 ratio 

 when selfed and the different types in the offspring segre- 

 gate in a characteristic fashion. 



In the tetraploids we may have a single extra chromo- 

 some in one set making a simple (4n + 1) mutant, or 2 

 chromosomes in a set making a simple (4w + 2) mutant. 

 We have two cases of a tetraploid with a deficiency in one 

 set, producing a (4ti — 1) mutant. 



Up to the present time, except for Gregory's work on 

 tetraploid Primulas (5) which was correctly interpreted 

 by Muller (6), Mendelian research has dealt almost ex- 

 clusively with disomic inheritance- Our work with the 

 jimsons and the recent investigations of Bridges on tri- 

 ploid Drosophilas offer an opportunity for tlu' ratluT 

 novel study of trisomic, tetrasomic and ix'utasoiiiic in- 

 heritance. We do not believe, however, that the jinison 

 weed is peculiar among plants in giving rise to chromo- 

 somal mutants. 



The unbalancing effect of the extra chromosomes can 

 best be illustrated by extra chromosomes in the Globe set. 

 The (2w + 2) Globe has two extra chromosomes in the 

 Globe set and hence should show a greater divergence 

 from normal than the Globe with only one extra chromo- 

 some. Such is the case. The simple {2n + 1) Globe (like 

 other mutants of this type) is less vigorous in growth 

 than normals. The (2*^ + 2) Globe is still less vigorous 

 than th^ more common {2n + 1) Globe. From tio-. 1 it will 

 be seen, further, that the Globe charactn - in the ( -n - 2) 

 Globe on the left, such as broadness of t fatn< >s of 

 bud, and density of foliage, are much further developed 



