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1903] BRIEFER ARTICLES 63 
in the shoot, while before the close of the 29 hours the zone of most 
rapid elongation had moved forward into the root. So far as con- 
cerned its geotropism it behaved as if all root. In older roots the 
growing region is shorter, as would be expected in correlation with 
their being decidedly more slender, and the curve is correspondingly 
nearer the tip. As the cotyledons serve solely as a food store, they 
remain in or on the ground, where the seed germinates, and there is 
no later growth with negative geotropism, such as occurs, for instance, 
in the hypocotyl of Lupinus. 
A hypocotyl is practically absent in the Aesculus seedling, the 
root beginning hardly a millimeter below the insertion of the petioles 
of the cotyledons. The lower part of these petioles, however, grows 
more or less firmly into a tube by the coalescence of their margins. 
The curve may occur in this tube, as in the figured and measured 
specimens, or in the upper ends where they are usually separate. The 
tube entirely surrounds the plumule, and the curve is ordinarily far 
enough up in the petioles so that the lower end of them with the 
enclosed plumule is brought into the vertical line with the root. 
The plumule being below the curve, and already in the vertical 
line, when it grows it does not escape from the petiole-tube by grow- 
ing out of the top of it, but out through its side. It does not have to 
force this passage, which it could hardly do. But at the height where 
it is to escape, and on that side, there is a vigorous but strictly local- 
ized growth, without a corresponding elongation elsewhere in the same 
zone. The result is the same as when the two guard cells of a stoma 
with rigid, fast ends enlarge ; they spread apart in the middle. In the 
Same way the two petioles pull, or rather push, apart, opening a wide 
crack, often two or three times as wide as it need be, to permit the free 
Srowth of the plumule. What stimulus determines this remarkable 
localized growth I do not know. 
This buckeye is very abundant here, and its large seeds with pow- 
erful roots make it an inviting subject for any work on the pressure 
exerted by the growing roots, or involving their mutilation. For these 
ordinary experiments on geotropism, reported here, it is well adapted, 
because it can easily be marked accurately, and -especially because of 
the ease of fixing the position. The cotyledons are so large and heavy 
that it is only necessary to make plane the proper side and put the 
Seedling down on that surface in a dish containing a little water. The 
Plane of the cut surface determines the inclination of the growing 
Tegion. If older seedlings are to grow downward, the cotyledons 
