98 JOHN HILL 



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 propa- 

 gate 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 experi- 

 ment, 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 Abrics 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 



