STUDIES ON THE GEOTROPISM OF STEMS. 
EDWIN BINGHAM COPELAND. 
1. The absence of polarity in the hypocotyl of Cucurbita. 
THE hypocotyl of Cucurbita, and, I suppose, of every plant 
whose cotyledons expand and act as leaves, is negatively geo- 
tropic in its ultimate reaction. When the hypocotyl is in any 
other position than the vertical, the under half of it grows more 
rapidly than the upper. This is regarded as a response to the 
unusual disposition of the burden of the parts of the hypocotyl, 
as they rest upon one another; and the seat of perceptivity and 
response is more specifically located in the green cortex." The 
purpose of the reaction is to get the cotyledons into the light, 
which, when the seed germinates in the ground, will be accom- 
plished by pushing them upward. Now it is evident without 
argument that an excess of growth of the under half of the 
hypocoty] will place its upper end in a vertical position, so that 
its further growth will be upward only in case the basal end is 
fixed in its position and the naturally upper end is free—a con- 
dition which is fulfilled in nature by a considerable growth of 
the root before the elongation of the shoot commences. 
Teleologically, perhaps phylogenetically, the geotropism of 
= shoot has been developed along lines of “lengthwise” pro- 
priety: 2. ¢., in order to secure a particular linear arrangement 
of root, hypocotyl, cotyledon, etc. But in the individual plant 
today, according to Czapek’s explanation (oc. cit.), which is the 
only rational one I am acquainted with, the response is to a dis- 
turbance of the normal “crosswise” arrangement, SO that each 
Srowing part of the hypocotyl acts without reference to the 
Parts more or less remote from the cotyledons. 
The question as to whether or not any trace of the develop- 
ment of geotropism remains in its manifestation in the present 
ac” F.: Weitere Beitrage zur Kenntniss geotropischen Reizbewegungen. 
- Wiss. Bot. 32: 248. 1898. 
we] 185 
