10 21. The Occurrence of a Rhythm in the geotropism of Two Species of Plankton Copepods when Certain Recurring External Conditions are Absent, by Calvin O. Esterly.
"The Subspecies of the Mountain Chickadee Vol. 17, No. 17, pp. 505-515"
Joseph Grinnell
What has been said in regard to animal heliotropism might, if space permitted, be extended, mutatis mutandis, to geotropism and stereotropism.
"Darwin and Modern Science"
A.C. Seward and Others
It must also be granted that geotropism has a bearing on the problem, since all plants twine upwards, and cannot twine along a horizontal support.
"Darwin and Modern Science"
A.C. Seward and Others