



1901] GEOTROPISM OF STEMS 4iI 
instance, by the disposition in many texts to substitute the word 
caulicle for radicle for the part of the embryo below the inser- 
tion of the cotyledons. In all Dicotyledons a part of the stem 
is distinguishable below the cotyledons, and in a majority it 
elongates to carry the cotyledons into the air. The elongation 
of the caulicle is the first visible growth. When the caulicle is 
largely a stem structure, and only the tip represents the future 
root, the beginning of growth is in the stem. In all cases the 
caulicle promptly bends downward. We have here apparently, 
then, positive geotropism of the hypocotyl, which so far as I 
know has not hitherto been recognized or investigated. 
Lupinus albus, in the size and uniformity of the seedlings and 
their rapid growth, is the best material I have found for this work. 
Both in the seed and on the seedling there is usually a well- 
defined line where the root merges into the stem. In the first 
cultures I marked this line with India ink on the swollen embryos, 
to be certain that it was the same one separating root and shoot 
in the seedling, and found that such was constantly the case. In 
order to have the entire descending axis free to curve, I usually 
removed the seedcoats, after swelling, but before any consider- 
able growth. This was not necessary for the mere demonstra- 
tion that a part of the hypocotyl bends downward, but when 
germination took place within the coats a part of the hypocotyl 
was often constrained by them. Their removal was probably 
without effect on germination or growth, though in an experi- 
ment to ascertain its influence the peeled plants grew slightly 
faster. 
One culture of plants is reported upon here in detail, to 
show the constancy of the results, and the range of variation 
that may be expected. The seeds were put into water 
‘October 1. On October 2, 9:00 A.M., the coats were removed. 
Fifteen very uniform embryos wefe selected and pinned with the 
axis horizontal. The length of the hypocotyl was 6™™, of the 
root 1.8™", The table shows the result after 24 hours. The 
_ last column, showing how far above the base of the hypocotyl 
the curve of least radius occurred, is the significant one. 
