1900] GEOTROPISM OF STEMS 189 
around indefinitely, as F. Darwin? did with the cotyledons of 
Sorghum. 
2. The geotropism of split stems. 
While it is certain that every growing part of the stem can 
perceive the geotropic stimulus and execute the response zm doco 
it is not impossible that if the local perceptivity could be inter- 
fered with, a growing zone might respond to a stimulus trans- 
mitted to it from another part of the plant. My first experiments 
with split hypocotyls were with a view to answering the question ; 
but they were not appropriate, because, as Sachs? showed, and as 
anybody can easily demonstrate, a half stem is in itself irritable. 
The results which they did yield, however, were surprising 
enough. 
Cucurbita —The first experiments were on Cucurbita hypo- 
cotyls, partly or wholly split, the split being either transverse or 
parallel to the plane of the cotyledons. Of three similar experi- 
ments it will suffice to report the following one, which began 
May 24, and lasted forty-eight hours. The growth is reported, 
and the angle made by the free end with its original horizontal 
position. 
Growth Curva- 
Growth Curva- in mm _ ture in 
in mm eo bes degrees 
Og Ba |S Split horizontal eo he 
2 Split vertical - wer 75 6 Split horizontal - ih. 165 
3 Split vertical : 4 70 +7 Split horizontal - 5 aoe 
4 Split horizontal - eo 
No. 1 was fastened in place without imbedding ; nos. 5 and 6 
had the cotyledons imbedded ; and the others, the roots. The 
ARWIN, in “ Botany at the British Association,” Nature 61 : 67. 
nt 
“a 
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iw 
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a 
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its y porotyl executes the response, he say ' 
cotyledon (which is fixed in a horizontal position) while the hypocotyl projects 
Bey 24 the b pocotyl begins to curve upward ... and it does not cease to 
ove when the free end points vertically upward ; the curvature continues indefinitely, 
oe the hypocotyl curls into a spiral of three or four rings.” 
aaa Ueber Wachsthum und Geotropismus aufrechter Stengel. ee 
low ungen 2:969. 1893. In the experiment Sachs reports, the growth o 
er half did not overcome the tissue tensions. 
Gesammelte 
