CHAP. X. APOGEOTROPISM. 509 



Verbena rose 90 in about 24 h. ; that of Bubus 67, 

 in 70 h. ; that of Cytisus 70, in 72 h. ; that of a young 

 American Oak only 37, in 72 h. The stem of a 

 young Cyperus alternifolius rose only 11 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 

 lepiophylla. 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 apo- 

 geotropism. 



A branch of Gucurbita ovifera, placed horizontally, 

 moved upwards during 7 h. in a straight line, until it 

 stood at 40 above the horizon ; it then began to cir- 

 cumnutate, 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 



