24 



BOTANY OF THE LIVING PLANT 



conditions kill the cell. These movements are then indications of life, 

 and their relations to temperature and other external conditions are 

 similar to those of other vital phenomena. 



Observations on the rapidity of the movements in the parenchyma of 

 the stem of Elodea in relation to temperature show that at o° C. there is 

 no movement. With a rise of temperature the mov^ement begins about 

 1° C. and increases in speed up to 36° C, which is the optimum. On further 

 raising the temperature the maximum is reached at 40° C, where movement 

 stops. The optimum and maximum temperatures in such cases appear to be 

 always near together. 



Turgor of the Cell. 



Such cells as these give evidence also of another important feature 

 common in the living cells of plants, viz. turgescence. If the length 

 of a cell of a living tissue be carefully measured in the normal con- 

 dition, and the cell be treated with a-5-iO per cent, solution of nitre, or 



Fig. 14. 



Young parenchymatous cell (i.) in the turgid state, (ii.) after treatment with 

 4 per cent, solution of nitre, (iii.) in 10 per cent, solution of nitre. a' = wall ; c = 

 cytoplasm ; 7i = nucleus ; s = cell-sap ; e= nitre-solution which has passed through 

 the cell-wall. (After De Vries.) 



of common salt, and measured again, it will be found that its length has 

 decreased. Its other dimensions would be found to have diminished 

 also (Fig. 14, i.-ii.). Presently it would also be seen that the cyto- 

 plasm had contracted away from the cell-wall. Frequently it rounds 

 itself off into an oval, highly refractive mass, occupying the middle of 

 the cell. This is the state styled plasmolysis (Fig. 14). If the effect 

 of the agent be watched, it will be seen that the shrinking of the cell 

 happens first, then that the cytoplasm separates from the angles of 

 the cells, and its contraction proceeds until, as it appears, a balance 



