VEGETABLE CYTOLOGY 
65 
Geotropism is the response of protoplasm to the stimulus of gravity. 
Roots of Pteridophytes and seed plants invariably grow downward 
toward the center of gravity and so are positively geotropic. The 
Fig. 30. —Venus fly-traps, Dioncea muscipula, growing in field near Wilmington, 
N. C. (Photograph by Charles Palmer.) 
fruiting organs of the fungi and the main stems of higher plants 
tend to grow perpendicular to the earth’s surface and so are nega¬ 
tively geotropic. Branches of stems that assume a relation parallel 
s 
