^68 LECTURE XXXIII. 



of volume, indicates how much the cell-walls were extended by the turgescence. As 

 I have aheady shown in Lecture XIII, and as is to be observed in the accompanying 

 figure (Fig. 353), the protoplasm becomes withdrawn from the cellulose wall through 

 the action of the solution (containing from 5-10 7o of salt), at first here and there, and 

 then on all sides, since the cell-sap gives up a great part of its water to the salt- 

 solution ; this latter penetrates through the cell- wall, but cannot enter into the pro- 

 toplasmic sac, but draws the water of the cell-sap from this : the sac thus contracts, 

 closely surrounding the cell-sap, which has now become more concentrated. The 

 pressure which the sap enclosed in the protoplasm previously exerted on the cellulose 

 wall herewith ceases, and the cell-wall left to itself then contracts back to its natural 

 size; its elastic contraction is here certainly less than that of the protoplasm, 

 relations which become clear at once on careful consideration of the accompanying 

 figure, borrowed from De Vries. It is also obvious that by means of feebler 

 action of a salt solution, or by feeble evaporation which acts in a strictly similar 



FIG. 353.— 1. Young, half'RTOwn cell from the cortical parenchyma of the peduncle of 

 Ctphalftrta ieucantha. 2. The same cell in a 4 'Yq solution of potassium nitrate. 3. The 

 same cpU in a 6 % solution. 4. The same cell in a 10 0^0 solution, i and 4 after nature; 

 2 and 3 diagrammatic. All in optical longitudinal section, k cell-wall ; p protoplasmic 

 lining of the wall ; k cell-nucleus ; 1: chlorophyll-grains ; J cell-sap ; e salt-solution which has 

 passed through the cell-wall (De Vries). 



manner, only a partial stoppage of turgescence will take place, no withdrawal of 

 the protoplasm from the cell-wall necessarily occurring at first; as soon, however, 

 as this does occur, even if only here and there, turgescence ceases. 



According to De Vries, if any part of the plant, young stem, or root, rendered 

 flaccid by plasmolysis, is again brought into pure water, the penetrated salt-solution 

 gradually soaks out, the protoplasmic sac again takes up pure water into its 

 interior, becomes distended, and applies itself on all sides to the interior of the 

 cellulose membrane, and as this assumption of water and absorption proceed further, 

 the cellulose membrane also becomes again extended, the condition of turgescence 

 begins anew, and the part concerned obtains practically the same volume, and 

 above all the same length, which it possessed before the investigation. That no 

 injury to the organ takes place, here the investigator named has sufficiently demon- 

 strated, and it is unquestionable that the object again becomes turgescent, and then 

 begins to grow anew, and that this growth may even be considerable. 



The importance of turgescence for growth — in other words, the importance 



