CHAP. X. GEOTROPISM. . 617 



Any one who will observe a flower-head burying itself, will be 

 convinced that the rocking rrovement, due to the continued 

 circumnutation of the peduncle, plays an important part in the 

 act. Considering that the flower-heads are very light, that tho 

 peduncles are long, thin, and flexible, and that they arise from 

 flexible branches, it is incredible that an object as blunt as one 

 of these flower-heads could penetrate the ground by means of 

 the growing force of the peduncle, unless it were aided by the 

 locking movement. After a flower-head has penetrated the 

 ground to a small depth, another and efficient agency comes into 

 play ; the central rigid aborted flowers, each terminating in five 

 long claws, curve up towards the peduncle; and in doing so 

 can hardly fail to drag the head down to a greater depth, aided 

 as this action is by the circumnutating movement, which con- 

 tinues after the flower-head has completely buried itself. The 

 aborted flowers thus act something like the hands of the mole, 

 which force the earth backwards and the body forwards. 



It is well known that the seed-capsules of various widely 

 distinct plants either bury themselves in the ground, or are 

 produced from imperfect flowers developed beneath the surface. 

 Besides the present case, two other well-marked instances will 

 be immediately given. It is probable that one chief good thus 

 gained is the protection of the seeds from animals which prey on 

 them. In the case of T. subterraneum, the seeds are not only 

 concealed by being buried, but are likewise protected by being 

 closely surrounded by the rigid, aborted flowers. We may the 

 more confidently infer that protection is here aimed at, because 

 the seeds of several species in this same genus are protected in 

 other ways ;* namely, by the swelling and closure of the calyx, 

 or by the persistence and bending down of the standard-petal, &c. 

 But the most curious instance is that of T. ylobosum, in which 

 the upper flowers are sterile, as in T. subterraneum, but are here 

 developed into large brushes of hairs which envelop and protect 

 the seed-bearing flowers. Nevertheless, in all these cases tho 

 capsules, with their seeds, may profit, as Mr. T. Thiselton Dyer 

 has remarked,t by their being kept somewhat damr and the 

 advantage of such dampness perhaps throws light on the pre- 

 sence of the absorbent hairs on the buried flower-heads of T. sub- 

 tenuueum. According to Mr. Bentham, as quoted by Mr. Bycr, 



* Vancher, 'Hist. Phys. (lea t See his interesting article ia 

 Hantes d'Europe,' torn. ii. p. 1 10. ' Nature,' April 4lh, 1878, p. 440 



