_ I1™" from the apex, may, in Zea mays, acc 
_ geotropism overcomes rheotropism, and the geotropl® 
280 BOTANICAL GAZETTE [APRIL 
geotropic stimulus, and thus gives a greater opportunity for the 
operation of rheotropism. When a root is displaced out of its 
position of geotropic equilibrium, the angle of ensuing geotropic 
curvature has been observed by many to begin, according to the 
diameter of the root, 2™™ to 3™" back from the apex. Roots, 
such as I have used for the most part, are 1.25™™ or less in diam- 
eter. Inthese, the geotropic angle is at first about 2™ from the 
apex; subsequently the curve extends backward, and includes 
several more proximal millimeters. We may follow the forma- 
tion of the §-shaped curve thus: The rheotropic curve begins in a 
Zea mays, according to Berg, in the 3d™™ from the apex; ee 
according to Juel in the 3d™™ of Vicia sativa. I have frequently 
seen it originate in the 2d™™ of both Brassica alba and Raphanus 
sativus, though in these plants it is often first seen in the 30" 
Berg’s, Juel’s, and my own observations agree in noting that the 
counter-curve generally does not appear till the rheotropic -" 
. ae oe angle pp oe g 45°. In one set of eight rheo- | 
tropically curving roots of Raphanus sativus, seven had bent to 45 
or over, and only one of these showed the dip of the tip. All ner 
observations show that the tip of the root, even the apical 2°. : 
may take a rheotropic curve. The part of the root farther wee 
begins to curve a little later, and a portion removed as ei 
ording to Berg, Pa 
ticipate in the rheotropic response. As the he see 
_ increases, the sensitive apex of the root comes oo nally 
. + . : : imulus, ¢ 
into positions of increasing gravitation sti de begins 
em 
to appear. As soon, however, as the tip declines, ae 
tion stimulus is less strongly felt and the rheotropic an 
now increase. This increase, however, is — so 
_ farther bending several millimeters distant from age” 
_ tip declining geotropically as the part behind a pif : 
_ tropically. This behavior, after the S-curve begins 9° dof the 
_ Teally implies a localization of the geotropic wena ! 
__ theotropic response in different parts of the Fone. on - 
: well worthy of special note, for by such initial so ; 
ta 
