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Show 568 SUMMARY AND CHAP. xu. upwards through 109° in 3 h. 8 m. Tho after-effects of apogeotropism last for above half an hour; and horizontally-laid hypocotyls are sometimes thus carried temporarily beyond an upright position. 'rhe benefits derived from geotropism, apogootropism, and diageotropism, are generally so manifest that they need not be specified. With the flower-peduncles of Oxalis, epinasty causes them to bend down, so that the ripening pods may be protected by the calyx from the rain. Afterwards they are carried upwards by apogeotropism in combination with hyponasty, and are thus enabled to scatter their seeds over a wider space. The capsules and flower-heads of some plants are bowed downwards through geotropism, and they then bury themselves in the earth for the protection and slow maturation of the seeds. This burying process is much facilitated by the rocking movement due to circumnutation. In the case of the radicles of several, probably of all seedling plants, sensitiveness to gravitation is con£.ned to the tip, which transmits an influence to the adjoining upper part, causing it to bend towards the centre of the earth. That there is transmission of this kind was proved in an interesting manner when horizontally extended radicles of the bean were exposed to the attraction of gravity for 1 or 1t h., and their tips were then amputated. Within this time no trace of curvature was exhibited, and the radicles were now placed pointing vertically downwards; but an influon.c~ ~ad already been transmitted from the tip to tho adJommg part, for it soon became bent to one side, in the s~me manner as would have occurred had the radwle remained horizontal and been still acted on by geotropism. Radicles thus treated continued to gr~w out horizontally for two or three days, until a new t1p was CHAP. XII. CONCLUDING REMARKS. 569 reformed ; and this was then acted on by t · . geo rop1sm, and the radwle became curved perpendicularly down-wards. It has now been shown that the following i~portant classes of movement all arise from modified circumnutation, which is omnipresent whilst growth lasts, and after growth has c~asod, "" honever pul vini arc present. These classes of movement consist of those d~e ~o epinasty and hyponasty,-those proper to chmbmg p~ants,. commonly called revolving nutation, -the nyct1tropw or sleep movements of loaves and cotyledons,-and the two immense classes of movement excited by light and gravitation. When we speak of modified circumnutation we mean that lio-ht or the alternations of light and darkness, gravitation: slight pressure or other irritants, and certain innate or constitutional states of the plant, do not directly caus~ ~he movement.; .the~ merely lead to a temporary mcrease or d1m1nutwn of those spontaneous changes in the turgescence of the cells which are already in progress. In what manner, light, gravitation, &c., act on the cells is not known ; and we will here only remark that, if any stimulus affected the cells ~n such a manner as to cause some slight tendency m the affected part to bend in a beneficial manner, this tendency might easily be increased through the preservation of the more sensitive individuals. But if such bending were injurious, the tendency would be eliminated unless it was overpoweringly strong ; for we know how common! y all characters in all organisms vary. Nor can we see any reason to doubt, that after the complete elimination of a tendency to bend in some ono direction under a certain stimulus, the power to bend in a directly |