STUDIES ON THE GEOTROPISM OF STEMS. II." 
EDWIN BINGHAM COPELAND. 
(WITH THREE FIGURES) 
THE review of my earlier papers on this subject, written by 
Czapek for the Botanische Zeitung, is in error on a point of 
priority and on the interpretation of the results. Sachs never 
showed that if a stem be split and the halves placed horizontal the 
under one would grow faster. In Sachs’ experiment referred to in 
the review the average elongation of the two faces of the upper 
half stem was 9.7™™, that of the lower half only 9.0™™. If the 
experiment had been continued longer (see footnote Bort. GAZ. 
29: 189. 1900) the relation would have been reversed. The 
review concludes: 
Insbesondere kann der Ref. sich der Ansicht des Verf. dass diese 
Erscheinung alle Theorien, welche den Sitz der geotropischen Reactionen 
in beiden Langshalften annehmen, ausser Kraft setze, nicht anschliessen. 
I-do not hold and have never expressed such a view. The 
phenomenon in question proves that both halves do share in the 
reaction, which therefore does not take ‘‘place entirely in either 
alf.””. As Czapek construed my conclusion, it is no wonder 
that he disagreed. 
3. Positive geotropism in the hypocotyl or cotyledon. 
The descending axis of a plant must grow and become fast in 
the ground before the negative geotropism of the ascending ax!s 
can result in the erection of the growing tip. That the former 
does break first from the seed is a matter of universal observa- 
tion. In the popular conception this first outgrowth is simply 
the “‘root;” but that this idea is not exact is recognized, for 
* The first number appeared in Bor. Gaz. 29: 185-196. 1900. 
? Bot. Zeit. 58: 200. 1900. 
410 [JUNE 
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