PROTOPLASMIC MOVEMENTS PLASMOLYSIS. 4:5 



larly in text-books, provide abundant illustrations of the two 

 methods of drawing. 



Now turn once more to the cell of the Tradescantia hair, and 

 endeavour with one or another drawing apparatus to make a 

 figure of it. As in all ordinary drawing apparatus 1 appliances 

 for the regulation of the light are wanting, so we must endeavour, 

 either by shading the drawing surface, or by changing the 

 position of the mirror, to obtain approximately similar brightness 

 for the drawing surface and the field of view of the microscope. 

 For drawing it is best to use stiff, smooth drawing-cards' 2 and 

 black lead pencils. In order that they shall not be effaced, 

 finished drawings can be washed over with very dilute gum- water. 



Protoplasmic Circulation, and Plasmolysis. Take in this way 

 a sketch of the general outline of the cell, of the cytoplasmic 

 streams and the nucleus, and compare it with the same cell after 

 the lapse of an hour, to see whether the form and general arrange- 

 ment now correspond. As already stated, we shall most probably 

 find that the distribution of the streams has altered, and that the 

 nucleus has changed its position in the cell. 



In order to determine that in their streaming the cells are 

 independent of one another, and that the cell-wall does not 

 influence the movement, allow a neutral but water-withdrawing 

 fluid to act upon the hair. From the edge of the cover-glass add 

 to the drop of water a little concentrated sugar solution, or better 

 still, glycerine. Before long the reagent begins to withdraw the 

 water of the cell- sap, and there results a decided contraction 

 of the cytoplasmic sac into the cell. This withdraws from certain 

 parts of the cell- wall. This contraction of the cytoplasmic body 

 of the cell under the influence of dehydrating media is distin- 

 guished by the name Plasmolysis. It can be then observed, 

 that so long as the contraction does not become too strong, the 

 streaming of the cytoplasm still goes on, even in those parts 

 where it has withdrawn from the cell-wall. Soon, however, all 

 movement in the cell is arrested. Yet in most cases to set it 

 going again it suffices to wash out the water- withdrawing reagent 

 by means of water. To this end water should be run under one 

 edge of the cover-glass, while the fluid under the cover-glass is 

 sucked out from the other edge by blotting-paper. The cytoplas- 



1 Excepting such as the best form of the Abbe-Zeiss. [Eo.] 



2 Such of excellent quality and surface are Goodall's thin Bristol Boards.' 

 -[ED.] 



