148 
GENETICS: A. F. BLAKESLEE 
Proc. N. A. S. 
order 7 into their squares in one of the two conformal groups. In the 
other group the reverse is true. Hence it is not possible to establish a 
simple isomorphism between the operators of these two groups. In 
view of the elementary properties of these groups it appears strange that 
the wide-spread error noted above was not corrected for more than a 
quarter of a century, especially since the incorrect results obtained by 
O. Holder have been used by various writers in extending his work. 
THE GLOBE, A SIMPLE TRISOMIC MUTANT IN DATURA 
By Albert F. BlakesIvEE 
Station for Experimental Evolution, Cold Spring Harbor, N. Y. 
Communicated by C. B. Davenport, March 10, 1921 
In a series of articles already published, 1 ' 2 ' 3 or at the present writing 
in press (American Naturalist, Genetics), a number of recurrent mutants 
discovered in the Jimson Weed (Datura Stramonium) have been described 
and their peculiarities in external appearance shown to be connected with 
the presence of one or more extra chromosomes in their nuclei. Evidence 
has been presented which indicates that a given mutant of the "simple 
trisomic" type is conditioned by the presence of a single extra chromosome 
in a specific one of the 12 chromosomal sets. Such a form is called a sim- 
ple trisomic mutant since in its somatic nucleus one of the 12 sets is a tri- 
some with three homologous chromosomes instead of all the sets being di- 
somes with two chromosomes each. The presence of an extra chromosome 
in a specific chromosomal set not only causes specific peculiarities in the 
growth and appearance of the mutant which results, but also brings 
about peculiarities in the inheritance of the mutant complex. 
It is the purpose in the present paper to summarize the findings in regard 
to one of the simple trisomic mutants — the Globe — in anticipation of a more 
detailed paper to be published shortly in Genetics. The data were accumu- 
lated for the most part before the chromosomal condition in the Globe and 
other simple trisomic mutants had been determined by my colleague, Mr. 
John Belling, from studies of mitotic figures in the pollen mother cells. 
The Globe was the first mutant recognized in the Jimson Weed, having 
been discovered in 1915. Its depressed globose capsules suggested the 
name. Its adult characters as well as the broad entire leaves of its seed- 
lings render the Globe one of the easiest mutants to recognize at any stage 
of development. It is the only one in fact that we have been able to pick 
out readily in the seed pan. Since usually it has not been necessary to 
grow plants beyond an early seedling stage when it is desired to distinguish 
Globes from normals, it has been possible with this mutant to base con- 
clusions on a larger number of individuals than could readily have been 
obtained if we had been dealing with the other mutant forms. 
