CHAP. X. GEOTKOPISM. 513 



almost straight course. A radicle of Cucurbita, directed 

 upwards (Fig. 26), also zigzagged at first, and de- 

 scribed small loops ; it then moved in a straight line. 

 Nearly the same result was observed with the radicles 

 of Zea mays. But the best evidence of the intimate 

 connection between circumnutation and geotropism 

 was afforded by the radicles of Phaseolus, Vicia, and 

 Quercus, and in a less degree by those of Zea and 

 ^sculus (see Figs. 18, 19, 21, 41, and 52) ; for when 

 these were compelled to grow and slide down highly 

 inclined surfaces of smoked glass, they left distinctly 

 serpentine tracks. 



The Burying of Seed-capsules : Trifolium subferraneum. The 

 flower-heads of this plant are remarkable from producing only 

 3 or 4 perfect flowers, which are situated exteriorly. All the 

 other many flowers abort, and are modified into rigid points, 

 with a bundle of vessels running up their centres. After a time 

 5 long, elastic, claw-like projections, which represent the divi- 

 sions of the calyx, are developed on their summits. As soon as 

 the perfect flowers wither they bend downwards, supposing the 

 peduncle to stand upright, and they then closely surround its 

 upper part. This movement is due to epinasty, as is likewise 

 the case with the flowers of T. repens. The imperfect central 

 flowers ultimately follow, one after the other, the same course. 

 Whilst the perfect flowers are thus bending down, the whole 

 peduncle curves downwards and increases much in length, 

 until the flower-head reaches the ground. Vaucher * says that 

 when the plant is so placed that the heads cannot soon reach 

 the ground, the peduncles grow to the extraordinary length of 

 from 6 to 9 inches. In whatever position the branches may be 

 placed, the upper part of the peduncle at first bends vertically 

 upwards through heliotropism ; but as soon as the flowers 

 begin to wither the downward curvature of the whole peduncle 

 commences. As this latter movement occurred in complete 

 darkness, and with peduncles arising from upright and from 

 dependent branches, it cannot be due to apheliotropism or to 

 epinasty, but must be attributed to geotropism. Nineteen 



* 'Hist. Phys. des Plantes d'Europe,' torn, ii, 1841, p. 106. 



