CHAPTER MODIFIED CIRCUMNUTATION: CLIMBING PLANTS; EPINASTIC AND HYPONASTIC MOVEMENTS
This chapter shows that geotropism, apogeotropism, and diageotropism are modified forms of circumnutation. It implies that gravitation produces some effect on the young tissues sufficient to serve as a guide to the plant. The chapter describes a few cases in which it may be how gradually circumnutation becomes changed into apogeotropism, under circumstances to be specified in each instance. When apogeotropism is rendered by any means feeble, it acts, as shown in the several foregoing cases, by increasing the always present circumnutating movement in a direction opposed to gravity, and by diminishing that in the direction of gravity, as well as that to either side. The most curious case known of a difference in sensitiveness to gravitation, and consequently of movement, in different parts of the same organ, is that offered by the petioles of the cotyledons of Ipomoea leptophylla. The chapter concludes that this moderately old joint was continually circumnutating on a small scale.