Feb., 1921] 
HARRIS AND OTHERS — SEEDLINGS OF PHASEOLUS 
65 
pairs of abnormal and normal seedlings were, in three of the lines investi- 
gated, derived from the same parent plant. 
Furthermore, care was taken that seedlings compared were grown 
under essentially identical conditions, in order to reduce to a minimum the 
environmental influences which might possibly tend to bring about dif- 
ferences between them. Seeds from individual plants were germinated 
in flats and harvested as soon as possible after they broke through the sand. 
Thus all seeds not only developed under the same parental environment but 
were germinated under sensibly identical conditions, were collected simul- 
taneously, and were in consequence sectioned at essentially the same stage 
of maturity. 
Because of the rapidity with which seedlings change and the great 
influence of temperature upon growth, it is difficult to standardize, or exactly 
to describe, the stage of development at which the seedlings were taken. 
Most of them were placed in alcohol before or very soon after the primordial 
leaves had unfolded. Thus a fairly uniform and early stage of development 
was secured. 2 
Free-hand sections were cut and mounted temporarily. When neces- 
sary, phloroglucin and hydrochloric acid were used to bring out the vascular 
bundles. The general vascular topography of the seedlings was studied, 
but the data for the statistical analysis of the seedling anatomy were 
derived from a careful count of the number of vascular bundles at various 
levels in the seedling. Because of a certain amount of variation in the 
number of bundles with position in the organ, counts were made in definite 
regions only — the basal region of the hypocotyl (just at the point of tran- 
sition from "root structure" to "stem structure"); the median region of 
the hypocotyl; and the median region of the epicotyl. In three series 
counts were also made of the protoxylem poles in the upper portion of the 
primary root. 
The number of data available for the several regions differs because of a 
change in the plan of the work. Sectioning and counting were begun by 
two of us at Cold Spring Harbor in the summer of 1917 and continued with 
the assistance of Miss Eunice Kinnear in the summer of 191 8. This w^ork 
was confined to the mid-regions of the hypocotyl and epicotyl. From a 
statistical study of these data it seemed desirable to have a further series 
of countings made independently by a specialist in vascular anatomy. 
The work was, therefore, continued at Storrs during 1918, 1919, and 1920. 
We are greatly indebted to Miss Flora Miller for assistance in this phase of 
the work. At Storrs, sections were made at the base of the hypocotyl as 
well as in the mid-region of hypocotyl and epicotyl. In three series, sections 
were made of the root as well. 
The bundles vary considerably in size, the largest being well developed 
2 Some of the seedlings of line 143 were allowed to become a little older, but there is no 
evidence of change in bundle number with age. 
