BRIBFER ARTICLES. 
POSITIVE GEOTROPISM IN THE PETIOLE OF THE 
COTYLEDON. 
(WITH ONE FIGURE) 
In a former paper’ on the geotropic responses of young hypocotyls 
and the cotyledons of some monocotyledons, I showed that the down- 
ward curves they execute are in response to stimuli received by the 
root tip. 
This note is to report the same phenomenon in yet another 
category of stem-organs—in the petiole of the cotyledon. 
The accompanying figure shows a seedling of Aesculus 
Californica. When the buckeye germinates, the first struc- 
tures to elongate are these petioles, and in whatever position 
the seed is lying they grow enough to bend in such a way 
that when the active growth of the root begins it is 
directly downward. I have observed the germination of 
the seeds in all cardinal positions and found this true, 
whether the curve was alike in the two petioles or was 
accomplished by more rapid growth of either one. 
The analogy to the positive geotropism in cotyledons 
and hypocotyls is close enough to convince one that these 
petioles act under the influence of the root tip. Measure- 
ments of the growing region corroborate this view. Ina 
rather advanced seedling, whose root was already 7” long 
at the beginning of the experiment, the growing region 
was more thanis5™" long. It was placed horizontal and left 
29 hours, and by that time the tip was aimed almost verti- 
cally downward. The most considerable elongation was in 
zones 6-8, but it amounted to 3™" (measured midway 
between the convex and concave sides) between the 10™ and 15™" 
lines. The curve began about the 14"™ mark, and had the least radius 
at about 12™", but continued toward the tip into zone 6. 
In this case there was evidently an apical growing region, consist- 
ing partly of root and partly of shoot, which curved where it grew. 
Likewise in both root and shoot the curvature was at first more largely 
* Bot. GAZ. 31: 410. 1901. 
62 [JULY 
Se RET te ee et 
