PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 8 FEBRUARY 15, 1922 Number 2 
STRUCTURAL CHANGES ASSOCIATED WITH FACTOR MUTA- 
TIONS AND WITH CHROMOSOME MUTATIONS 
. IN DATURA 1 
By Edmund W. Sinnott and Ai^bhrt F. BIvAKESlkk 
Connecticut AgricuivTurai. College, Storrs, Conn., and Station for Experi- 
mental Evolution, Cold Spring Harbor, Long Island, N. Y. 
Communicated by C. B. Davenport, January 14, 1922 
The fact has recently been emphasized^ that two distinct types of muta- 
tion may occur in plants — those which are due to the change of a single 
factor or gene and those which are due to the addition of one or more 
entire chromosomes. The Jimson Weed, Datura Stramonium , displays 
both of these mutation types. If we consider the purple-flowered, spiny 
fruited, many-noded form the primitive type, three "factor" mutations 
have occurred, giving rise to white-flowered, smooth-fruited, and few- 
noded types; and twelve distinct "chromosome" mutations have been 
identified and named, each of which has been found to be associated with 
the addition of an extra chromosome to a particular one of the twelve 
pairs. Tetraploid plants and other chromosomal aberrations have also 
been found. 
These mutations have been identified by various external characters. 
The purpose of the present investigation (of which this paper is a pre- 
liminary report) is to study and compare the structure of these mutant 
forms, both as to gross external morphology and as to internal anatomy; 
and thus to determine the structural effects produced by a single factor 
and those produced by a single entire chromosome. In this way it may 
be possible to begin an analysis of the factorial constitution of each of the 
chromosomes. 
Externally, various measurements of the gross structure of the plant 
body were made. Branching in the Jimson Weed is essentially dicho- 
tomous and the two branches are usually of decidedly different lengths. 
These measurements were of (1) the trunk length (height of stalk to the 
first fork; (2) the width of the angle formed by the branches at the first 
17 
