Different species and different parts of the same species are acted on by apogeotropism in very different degrees.  Young seedlings, most of which circumnutate quickly and largely, bend upwards and become vertical in much less time than do any older plants observed by us; but whether this is due to their greater sensitiveness to apogeotropism, or merely to their greater flexibility we do not know.  A hypocotyl of Beta traversed an angle of 109o in 3 h. 8 m., and a cotyledon of Phalaris an angle of 130o in 4 h. 30 m.  On the other hand, the stem of a herbaceous [page 509] Verbena rose 90o in about 24 h.; that of Rubus 67o, in 70 h.; that of Cytisus 70o, in 72 h.; that of a young American Oak only 37o, in 72 h.  The stem of a young Cyperus alternifolius rose only 11o in 96 h.; the bending being confined to near its base.  Though the sheath-like cotyledons of Phalaris are so extremely sensitive to apogeotropism, the first true leaves which protrude from them exhibited only a trace of this action.  Two fronds of a fern, Nephrodium molle, both of them young and one with the tip still inwardly curled, were kept in a horizontal position for 46 h., and during this time they rose so little that it was doubtful whether there was any true apogeotropic movement.

The most curious case known to us 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 basal part for a short length where united to the undeveloped hypocotyl and radicle is strongly geotropic, whilst the whole upper part is strongly apogeotropic.  But a portion near the blades of the cotyledons is after a time acted on by epinasty and curves downwards, for the sake of emerging in the form of an arch from the ground; it subsequently straightens itself, and is then again acted on by apogeotropism.

A branch of Cucurbita ovifera, placed horizontally, moved upwards during 7 h. in a straight line, until it stood at 40o above the horizon; it then began to circumnutate, as if owing to its trailing nature it had no tendency to rise any higher.  Another upright branch was secured to a stick, close to the base of a tendril, and the pot was then laid horizontally in the dark.  In this position the tendril circumnutated and made [page 510] several large ellipses during 14 h., as it likewise did on the following day; but during this whole time it was not in the least affected by apogeotropism.  On the other hand, when branches of another Cucurbitaceous plant, Echinocytis lobata, were fixed in the dark so that the tendrils depended beneath the horizon, these began immediately to bend upwards, and whilst thus moving they ceased to circumnutate in any plain manner; but as soon as they had become horizontal they recommenced to revolve conspicuously.* The tendrils of Passiflora gracilis are likewise apogeotropic.  Two branches were tied down so that their tendrils pointed many degrees beneath the horizon.  One was observed for 8 h., during which time it rose, describing two circles, one above the other.  The other tendril rose in a moderately straight line during the first 4 h., making however one small loop in its course; it then stood at about 45o above the horizon, where it circumnutated during the remaining 8 h. of observation.