510 MODIFIED CIECUMNUTATION. CHAP. X. 



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 re- 

 commenced 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 45 above the horizon, where it circum- 

 nutated during the remaining 8 h. of observation. 



A part or organ which whilst young is extremely 

 sensitive to apogeotropism ceases to be so as it grows 

 old ; and it is remarkable, as showing the independence 

 of this sensitiveness and of the circumnutating move* 

 ment, that the latter sometimes continues for a time 

 after all power of bending from the centre of the earth 

 has been lost. Thus a seedling Orange bearing only 

 3 young leaves, with a rather stiff stem, did not curve 

 in the least upwards during 24 h. whilst extended 

 horizontally ; yet it circumnutated all the time over 

 a small space. The hypocotyl of a young seedling 

 of Cassia tora, similarly placed, became vertical in 

 12 h. ; that of an older seedling, 1^ inch in height, 



* For details see The Movements and Habits of Climbing Plants, 

 1875, p. 131. 



