520 MODIFIED CIRCUMNUTATION. CHAP. X. 



minal bleached portion was a little shrivelled. As the gyno- 

 phores are rigid and arise from stiff branches, and as they 

 terminate in sharp smooth points, it is probable that they could 

 penetrate the ground by the mere force of growth. But this 

 action must be aided by the circumnutating movement, for fine 

 sand, kept moist, was pressed close round the apex of a gyno- 

 phore which had reached the ground, and after a few hours it 

 was surrounded by a narrow open crack. After three weeks 

 this gynophore was uncovered, and the apex was found at a 

 depth of rather above half an inch developed into a small, white, 

 oval pod. 



Amphicarpcea monoica. This plant produces long thin shoots, 

 which twine round a support and of course circumnutate. 

 Early in the summer shorter shoots are produced from the 

 lower parts of the plant, which grow perpendicularly downwards 

 and penetrate the ground. One of these, terminating in a 

 minute bud, was observed to bury itself in sand to a depth of 

 0'2 inch in 24 h. It was lifted up and fixed in an inclined 

 position about 25 beneath the horizon, being feebly illuminated 

 from above. In this position it described two vertical ellipses 

 in 24 h. ; but on the following day, when brought into the house, 

 it circumnutated only a very little round the same spot. Other 

 branches were seen to penetrate the ground, and were after- 

 wards found running like roots beneath the surface for a length 

 of nearly two inches, and they had grown thick. One of these, 

 .after thus running, had emerged into the air. How far circum- 

 nutation aids these delicate branches in entering the ground we 

 do not know ; but the reflexed hairs with which they are clothed 

 will assist in the work. This plant produces pods in the air, 

 and others beneath the ground ; which differ greatly in appear- 

 ance. Asa Gray says * that it is the imperfect flowers on the 

 creeping branches near the base of the plant which produce the 

 subterranean pods; these flowers, therefore, must bury them- 

 selves like those of Arachis. But it may be suspected that the 

 branches which were seen by us to penetrate the ground also 

 produce subterranean flowers and pods. 



DlAGEOTKOriSM. 



Besides geotropism and apogeotropism, there is, 

 according to Frank, an allied form of movement, 



* Manual of the Botany of the Northern United States,' 1856, p. 106. 



