100 Newcombe, Gravitation sensitiveness not confined to apex of root. 



of geotropic sensitiveness by more than 2 mm of the root-tip. 

 That the part of the root posterior to the 2 apical millimeters is 

 sensitive to gravitation will be shown in the second part of 

 this paper. 



Part II. Demonstration of gravitation sensitiveness thru more 

 than four millimeters of the root-tip. 



In the flrst part of this paper it has been shown that the 

 peculiar behavior of roots when subjectecl to the conditions imposed by 

 Czapek, Fr. Darwin, Nemec, Andrews, Cholodnyj and others 

 may be accounted for not only by the hypothesis of the restriction 

 of the sensory region to the apical one or two millimeters, but 

 just as well by the hypothesis of the possession of geotropic sen- 

 sitiveness by the whole elongating region of the root, with the 

 sensitiveness decreasing from the punctum vegetationis pos- 

 teriorly. The ensuing pages will be devoted to a record of ex- 

 periments which will show that the latter of the two hypotheses 

 is the correct one, or, at least, will disprove the assumption of 

 Darwin, that sensitiveness is localized in the tip of the root. 



Since, as has already been pointed out, any method which 

 depends for results on the bending of the apical 2 millimeters of 

 the intact root into a different angle than that of the more pos- 

 terior portion must fail to lead to a Single hypothesis, some other 

 method of experimentation must be used. That employed by 

 Piccard 1 ) would seem a little too precarious to be satisfactory. The 

 old method of beheading roots and then laying them horizontal, 

 to determine whether by the possible geotropic sensitiveness of 

 the part left the root would curve downward, is generally con- 

 demned; for there is reason for supposing that the wounding dis- 

 turbs or inhibits the normal behavior. This method led Darwin 

 to believe that the sensitive region was confined to the apical 

 one or two millimeters, and led Wiesner to reject that view. 

 Eoots so treated either do not bend at all or bend too irregularly 

 to allow safe conclusions to be drawn. 



Eeflection on these matters brought the thought that, if more 

 than the apical 2 millimeters of the root were sensitive to gravi- 

 tation, a gravitation Stimulus above the normal might overcome 

 the autotropism and the effect of wounding sufticiently to bring 

 the geotropism of decapitated roots to expression. This notion 

 seemed all the more probable from the demonstration of Sachs 2 ), 

 Czapek 3 ) and others that a more than normal gravitation Stimu- 

 lus brings a greater than normal geotropic response. The centri- 



x ) Neue Versuche, über die geotropische Sensibilität der Wurzelspitze. 

 (Jahrb. wiss. Botanik. XL. 1904. 94.) 



2 ) Wachstum der Haupt- und Nebenwurzeln. (Arbeiten d. bot. Inst. 

 Würzburg. I. 1874. 607.) 



3 ) Untersuchungen über Geotropismus. (Jahrb. wiss. Botanik. XXVII. 

 1895. 301.) 



