104 CARNEGIE INSTITUTION OF WASHINGTON. 



This work requires the cooperation of many sorts of workers: (1) 

 The analyst who makes the matings and coordinates the results; this 

 part of the work is in the hands of Dr. Blakeslee. (2) The cytologist, 

 who studies the chromosomal complex (number and form) associated 

 with each somatic variant and the distribution of chromosomes in 

 hybrids and their progeny. (3) The student of pollen and pollen- 

 tube growth, to test on the one hand pollen sterility and on the other 

 that of differential growth, and, hence, differential fertilization. (4) 

 The analyst of the elements of somatic form. (5) The chemist, who 

 should study the chemical differences associated with differences in 

 form. 



General Account of the Datura Mutants. 



A preliminary report on the jimson weed (Datura) was made by 

 Blakeslee, Belling, and Farnham in Science, October 22, 1920, under the 

 title "Chromosomal duplication and Mendelian phenomena in Datura 

 mutants." In this paper it is pointed out that just as there are 12 

 chromosomes (A, B . . . . K, L) in the gametes so there are 12 

 mutants from the normal form, in each of which 1 extra chromosome 

 is present; and evidence is presented that in each of the 12 mutants 

 the extra chromosome is a different one; i. e., in one there is an extra A, 

 in another an extra B, and so on. Of the pollen grains of these mutants, 

 half have 12 chromosomes and half have 13; and evidently the same is 

 the case in the egg cells; but apparently the pollen with 13 nuclei is 

 non-functional. The authors announce also the discovery of triplets 

 in place of pairs of every kind of chromosome; and also a case of 

 quadrupled (tetraploid) chromosomes. 



Dr. Blakeslee reports that the field records of the present season are 

 not yet complete, but the data so far obtained warrant a classification 

 of the known mutant types according to their chromosomal constitu- 

 tion as shown in table 1 and diagrams (fig. 1). 



Dr. Blakeslee proceeds: 



"The classification adopted was suggested in a recent paper in the Amer- 

 ican Naturalist. 



"Of the unbalanced types, the first mutants discovered were simple tri- 

 somic diploids due to an extra chromosome in a single set. Last year we had 

 gained evidence which indicated that Poinsettia is the mutant that has the extra 

 chromosome in the s( t carrying the factors for purple and white flower color. 

 This evidence, from tlie peculiar ratios obtained when these Mendelian char- 

 acters are transmitted, has been increased by further data acquired this year. 

 By similar breeding evidence it is rendered highly probable that Cocklebur 

 is the mutant with an extra chromosome in the set carrying factors for spini- 

 ness of capsules. 



"Triploids have been secured by crossing tetraploids with normals. 



"The double trisomic diploids have been secured in the offspring from 

 triploids. Since in the latter each set has 3 chromosomes, the gametes will 

 receive from each set either 1 or 2 chromosomes at reduction division. In 

 consequence, the types of gametes produced by triploids by the theory of 

 chance should correspond to a binomial expansion and we should have in 



