42 Macfarlane. — Contributions to the History of 



living cell protoplasm is the direct and active agent ? First, it 

 is to be remembered, that since the cell walls are traversed 

 by pores, the protoplasmic threads either must act as perfect 

 plugs to prevent general diffusion of liquids between the 

 cells, or the cells that are traversed by pores must be cut off 

 in the unexcited state from the intercellular spaces, or from' 

 other cells that are not provided with pores, if such exist. 

 Otherwise none of the walls could become tense. 



It appears to be more in accordance with our present 

 knowledge if we regard the protoplasmic utricle as the layer 

 which can retain or give off its contents according to its 

 molecular condition, and that the cellulose membranes are 

 merely secondary strengthening sacs that act much like the 

 netting bags which surround rubber bellows. Our reasons 

 for this opinion are that the summation results, the effects of 

 different chemical agents, and of energy in varying forms 

 demonstrate a gradual and very exact contraction of the pro- 

 toplasm, with corresponding contraction of the leaf substance. 



Now, if this be accepted as a working hypothesis only, the 

 question arises as to how the protoplasmic utricle of the cell 

 is affected by stimuli. It is manifest that some change in the 

 leaf cells follows stimulation of the hairs, and in view of their 

 structure and relations this seems to be largely propagated, or 

 distributed from the columnar cells that form the joint of the 

 hair. We would suggest that, on first mechanical stimulation 

 of the leaf, or stimulation of it by chemical, thermal, or other 

 action that the protoplasm of each cell at once rearranges local- 

 ized groups of its molecules so as to form little permeable areas 

 for the contained sap. This may constitute the change that 

 succeeds first mechanical stimulus. But on second stimulus 

 or continued chemical or electrical stimulus, alteration and 

 aggregation of all the molecules causes contraction of the 

 utricle and squeezing out of liquids through the pores or 

 permeable areas, already established, a certain quantity being 

 speedily expelled through the pores of the hair-joint cells, if 

 such exist. In any case, we agree with Gardiner that the 

 cause of movement is to be sought for in protoplasmic 

 activity, which exhibits itself in permitting or prohibiting 



