Geotropic Response at Various Angles of Inclination. 
BY 
FREDERICK C. NEWCOMBE. 
University of Michigan. 
A. Angle for Maximum Response of Primary Roots and Stems. 
I. Introduction. 
I N his fundamental work on the growth of roots, Sachs 1 gives as the 
second of his three laws for the curvature of roots, that zones of 
equal development show various angles of curvature in the same time if the 
roots are placed at various angles with the vertical, and the curvature 
becomes the stronger the nearer the axis of the root is placed to the 
horizontal. Sachs does not give a very firm basis for this law, since he 
does not cite specific experiments from which the reader may judge the 
evidence. One finds, however, here and there a statement from which it is 
learned that Sachs laid seedlings at various angles of inclination, noting the 
latent period of curvature and the angles attained in given periods of time. 
Bateson and F. Darwin 2 tested the detached inflorescence-stalks of 
Plantago lanceolata and of Brassica oleracea by fastening them at various 
angles of inclination, allowing them so to remain for two hours, then 
releasing them and laying them horizontally under water so that their 
former right and left sides became the upper and lower. The angle of 
curvature after one hour was taken as an index of the strength of geotropic 
stimulation. The results agreed wholly with those of Sachs on roots, in 
finding the strongest curves in those stems which had been kept horizontal. 
Czapek 3 next took up the problem with both roots and stems. His 
method consisted in tying the plant members to rods of wood or glass, or 
encasing them in closely-fitting glass tubes, and thus exposing them to 
gravitation stimulation for periods of three to six hours at temperatures 
of 17 0 to 1 9 0 . The objects were then released and rotated on the klinostat 
for twenty-four hours, when the angles caused by the gravitation stimulation 
were measured and used as an index of relative intensity of response. In 
this way Czapek tested the roots of Lupinus , Vida Faba> Phaseolus , Pisum 
and Zea , the hypocotyl oiHelianthus , and the sporangiophores of Phycomyces. 
As a general result the author states that the greatest angles were formed 
1 Ueber das Wachsthum der Haupt- und Nebenwurzeln. Arbeit, bot. Inst. Wtirzb., i, 1873, p. 454. 
2 ‘ A Method of Studying Geotropism.’ Ann. of Bot., ii, 1888, p. 65. 
3 Untersuchung iiber Geotropismus. Jahrb. f. wiss. Bot., xxvii, 1895, p. 283. 
[Annals of Botany, Vol. XIX. No. LXXIV. April, 1905.] 
