100 Newcombe, Gravitation sensitiveness not confined to apex of root, 
of geotropic sensitiveness by more tban 2 mm of tbe root-tip. 
Tha"t tbe part of tbe root posterior to tbe 2 apical millimeters is 
sensitive to gravitation will be sbown in tbe second part of 
tbis pap er. 
Part II. Demonstration of gravitation sensitiveness thru more 
than four millimeters of the root-tip. 
In tbe first part of tbis paper it bas been sbown tbat tbe 
pecnliar bebavior of roots wben subjected to tbe conditions imposed by 
Czapek, Fr. Darwin, Nemec, Andrews, Cbolodnyj andotbers 
may be accounted for not only by tbe bypotbesis of tbe restriction 
of tbe sensory region to tbe apical one or two miUimeters, bnt 
just as well by tbe bypotbesis of tbe possession of geotropic sen¬ 
sitiveness by tbe wbole elongating region of tbe root, witb tbe 
sensitiveness decreasing from tbe punctum vegetationis pos- 
teriorly. Tbe ensuing pages will be devoted to a record of ex- 
periments wbicb will sbow tbat tbe latter of tbe two bypotbeses 
is tbe correct one, or, at least, wiU disprove tbe assumption of 
Darwin, tbat sensitiveness is localized in tbe tip of tbe root. 
Since, as bas already been pointed out, any metbod wbicb 
depends for results on tbe bending of tbe apical 2 millimeters of 
tbe intact root into a different angle tban tbat of tbe more pos¬ 
terior portion mast fail to lead to a single bypotbesis, some otber 
metbod of experimentation must be nsed. Tbat employed by 
Piccardi) would seem a nttle too precarious to be satisfactory. Tbe 
old metbod of bebeading roots and tben laying tbem horizontal, 
to determine wbetber by tbe possible geotropic sensitiveness of 
tbe part left tbe root would cnrve downward, is generally con- 
demned; for tbere is reason for supposing tbat tbe wounding dis- 
turbs or inbibits tbe normal bebavior. Tbis metbod led Darwin 
to believe tbat tbe sensitive region was confined to tbe apical 
one or two miUimeters, and led Wiesner to reject tbat view. 
Eoots so treated eitber do not bend at aU or bend too ii’regularly 
to aUow safe conclnsions to be di’awn. 
Eeflection on tbesematters brongbt tbe tbougbt tbat, if more 
tban tbe apical 2 miUimeters of tbe root were sensitive to gravi¬ 
tation, a gravitation Stimulus above tbe normal migbt overcome 
tbe autotropism and tbe efiect of wounding sufticiently to bring 
tbe geotropism of decapitated roots to expression. Tbis notion 
seemed aU tbe more probable from tbe demonstration of Sacbs^), 
Czapek 2) and otbers tbat a more tban normal gravitation Stimu¬ 
lus brings a greater tban normal geotropic response. Tbe centri- 
1) Neue Versuche über die geotropische Sensibilität der Wurzelspitze. 
(Jabrb. wiss. Botanik. XL. 1904. 94.) 
2) Wachstum der Haupt- und Nebenwurzeln. (Arbeiten d. bot. Inst. 
Würzburg. I. 1874. 607.) 
2) Untersuchungen über Geotropismus. (Jabrb. wiss. Botanik. XXV11. 
1895. 301.) 
