Page:Makers of British botany.djvu/132

 98 and a closing sideways; which the direction and course of the fibres also favours: in the Parkinsonia they are smaller, and yet more compact; and the consequence of this is, that its lobes have no farther possible motion, than the expanding upwards."

Again, "The clusters of fibres are as a kind of joints on which their lobes are capable, under the influence of light, of a certain limited motion."

Further, with regard to Mimosa, he remarks that "To propagate the motion when the leaves are in a state to shew it, there requires a perfect and confirmed state of those clusters of fibres lodged at their base." Hill then describes the experiments upon which he based his conclusions; these shew that he was fully awake to the importance of keeping the conditions of an experiment, other than those of light, as near constant as possible, and that the position assumed by the leaves depends upon the intensity of the light.

His final experiment was to place the Abrus in a bookcase in such a position that the sun shone full upon it; when the leaves were fully expanded he closed the doors and found that in an hour "The lobes were all drop't, and it was in the same state that it would have shewn at midnight. On reopening the doors the elevated position of the leaves was assumed in twenty minutes."

Hill offers the same explanation of the movements of Mimosa as of those exhibited by Abrus, the reason for their greater conspicuousness in the former plant being due to the fact that in Mimosa "As there are no less than three sets of these clusters [of fibres which are placed at the bases of the foot-stalks], the effects of the same principle are naturally much greater than in the Abrus where there is only one."

Hill carefully observed the sequence of motion in the Mimosa, and points out that the effect of absolute darkness on the plant is greater than the rudest touch. He also found that the contact stimulus must be of a sufficient intensity, and that the degree of the subsequent motion depended upon the potency of the stimulus. He further observed that shaking the plant had the same effect as contact stimulation; also he remarks upon the