Arachis hypogoea.—­The flowers which bury themselves, rise from stiff branches a few inches above the ground, and stand upright.  After they have fallen off, the gynophore, that is the part which supports the ovarium, grows to a great length, even to 3 or 4 inches, and bends perpendicularly downwards.  It resembles closely a peduncle, but has a smooth and pointed apex, which contains the ovules, and is at first not in the least enlarged.  The apex after reaching the ground penetrates it, in one case observed by us to a depth of 1 inch, and in another to 0.7 inch.  It there becomes developed into a large pod.  Flowers which are seated too high on the plant for the gynophore to reach the ground are said* never to produce pods.

The movement of a young gynophore, rather under an inch in length and vertically dependent, was traced during 46 H. by means of a glass filament (with sights) fixed transversely a little above the apex.  It plainly circumnutated (Fig. 193) whilst increasing in length and growing downwards.  It was then raised up, so as to be extended almost horizontally, and the terminal part curved itself downwards, following a nearly straight course during 12 h., but with one attempt to circumnutate, as shown in Fig. 194.  After 24 h. it had become nearly vertical.  Whether the exciting cause of the downward movement is geotropism or apheliotropism was not ascertained; but probably it is not apheliotropism, as all the gynophores grew straight down towards the ground, whilst the light in the hot-house entered from one side as well as from above.  Another and older gynophore, the apex of which had nearly reached the ground, was observed during 3 days in the same manner as the first-mentioned short one; and it was found to be always circumnutating.  During the first 34 h. it described a figure which

* ‘Gard.  Chronicle,’ 1857, p. 566. [page 519]

represented four ellipses.  Lastly, a long gynophore, the apex of which had buried itself to the depth of about half an inch, was

Fig. 193 Arachis hypogoea:  circumnutation of vertically dependent young gynophore, traced on a vertical glass from 10 A.M.  July 31st to 8 A.M.  Aug. 2nd.

Fig. 194.  Arachis hypogoea:  downward movement of same young gynophore, after being extended horizontally; traced on a vertical glass from 8.30 A.M. to 8.30 P.M.  Aug. 2nd.

pulled up and extended horizontally:  it quickly began to curve downwards in a zigzag line; but on the following day the ter-[page 520] minal bleached portion was a little shrivelled.  As the gynophores 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 gynophore 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.