204 



BIOLOGIC A L LECTURES. 



Some botanists have attempted to distinguish between plants 

 that show a heat-sleep with the leaflets directed upwards, and 

 a night-sleep in which they fall down, as compared with others 

 that have the same position alike in heat and sleep. But here 

 is a plant which folds upwards its seed leaves, and downwards 

 its folia2:e leaves under all kinds of stimuli. 



In such a condensed statement as I now give, it would be 

 impossible to dwell on the anatomical details of the species 

 already named. Suffice it that they all exhibit beautiful 

 intercellular protoplasmic unions from cell to cell, as was first 

 demonstrated for the sensitive plant by Gardiner. 



We may now attempt shortly to answer the question, How 

 are the irrito-contractile movements originated and propagated, 

 and what are the cell changes which accompany them .^ Until 

 within the last decade, botanists were compelled to view living 

 vegetable cells as organic units that were sharply demarcated 

 from each other by cellulose walls, and whose life phenomena 

 were due to protoplasmic activity of each cell. J>ut no matter 

 how complex and intricate the chemical changes that were 

 effected, they still viewed the protoplasm as a rather watery 

 substance of no great consistency, tenacity, or structural 

 complexity. The study of nuclear changes during new cell 

 formation, of the existence of sensitive movements in different 

 plants, but especially the demonstration of intercellular proto- 

 plasmic threads that link together the cell protoplasms into 

 one harmonized body, compel us to accept the conclusion that 

 the protoplasm of a vacuolated cell is a very complex and 

 resistant substance that is extremely responsive to environ- 

 mental stimuli. Still, with few exceptions — and chief among 

 these we reckon Gardiner of Cambridge — botanists clung, 

 and even now cling, to the idea that irrito-contractile move- 

 ments are simjily, or at least chiefly, due to migration of cell 

 sap from a living cell or cells into intercellular spaces, owing 

 to contraction of the cellulose walls. Sachs, Bert, Niigeli and 

 Schwendener, Pfeffer and DeVries have propounded the view 

 that contraction of the walls is the important factor. 



The untenableness of this position is being gradually recog- 

 nized, and one can see that a change is coming. The 



