98 CARNEGIE INSTITUTION OF WASHINGTON. 



In order to obtain an idea of the distribution of chromosomal types in the off- 

 spring of An and of (4w+ 1) and (4?i+2) forms, a cytologtcal study is being made 

 of certain pedigrees from such parents by Dr. Belling, whose report is given 

 on page 99 It may be said, however, that the type of disjunction for normal 

 tetraploids with 48 chromosomes has been established and found to be dis- 

 tinctly different from that for certain 48 chromosome forms which, both from 

 the somatic appearance, with ovate instead of spherical capsules, and from 

 the breeding behavior, had been believed to be of the type (4n+l — 1) with a 

 chromosome deficiency in one set numerically compensated by an excess in 

 another. The study shows that of two plants, each with 48 chromosomes, 

 one may be a true An tetraploid, while the other may be a modified tetraploid 

 with two sets differently affected." 



A summary may be given of the chromosomal types already identified. 

 In most cases their chromosomal counts have been determined by Dr. Belling, 

 though in a few instances they have been recognized by morphological appear- 

 ance and breeding behavior. In the 4 balanced types (In, 2n, 3n, An) the 4 

 forms theoretically possible have been identified. In each of the unbalanced 

 types with one set affected, 12 forms are theoretically possible, and we have 

 identified the following: (2n+l), (2n-l), (2n+2), (3n+l), (3n-l), (4n+l), 

 (An— 1), (4n+2), (4n+3). Of each of the unbalanced types with 2 sets 

 similarly affected, 66 forms are theoretically possible, and we have identified 

 the following: (2/1+1 + 1), (4n+l + l), (4n-l-l). In each of the un- 

 balanced types with 3 sets similarly affected, 220 forms are theoretically 

 possible, but we have identified only one form of the type (2n+ 1 + 1 + 1). In 

 addition, we have identified a form of the type (4w+l — 1) of which there are 

 132 forms theoretically possible, and one form of the type (4n+l + l — 1 — 1) 

 of which there are 2,970 forms theoretically possible. In the above summary 

 only "apostles" are considered. If the "acolytes" were included, the number 

 of possible forms would be greatly increased. It is obvious that an enormous 

 number of forms are theoretically possible by aberrations in chromosome 

 number. Only the even-balanced types can be expected to breed true, but 

 the other types could be propagated vegetatively if they were of sufficient 

 economic importance. 



"An effort has been made to induce mutations in the jimson weeds by 

 various external stimuli. Of the (2n+ 1) mutants derived from capsules which 

 had been subjected to radium rays by Dr. Gager, one (a microcarpic plant) 

 produced when selfed an offspring with about one-fourth of the individuals 

 albinos, which died as seedlings. The inheritance of this albino character is 

 being investigated. Its origin is possibly due to the radium treatment. Cold 

 is a stimulus which has a very marked effect upon the formation of at least the 

 male gametophjrtes. By its use we have been able to induce non-reduction 

 and disturbances in chromosome disjunction, as indicated by the production 

 of a large number of giant pollen-grains, an increase in the percentage of bad 

 grains, and a wide variation in the size of good grains, and finally the entire 

 abortion of the pollen. The seeds obtained by selfing plants thus treated with 

 cold have given rise, among other mutant types, to 5 haploid and 2 tetra- 

 ploid seedlings, but, in the majority of the cases at least, apparently the 

 rough and poorly controlled treatment did not happen to reach the female 

 gametes at the critical stage, and it is the female rather than the male 

 gametes which are effective in initiating mutations. We believe that with 

 more accurately regulated cold-temperature rooms it would be possible to 

 control the production of mutants by means of cold treatment." 



