MICRO-PHYSICS OF THE CELL. 37 



either in the cells or at their edge, which are readily 

 soluble in water. The best method is to maintain a 

 stream of alcohol under the cover-slip by means of 

 blotting-paper. 



A saturated solution of asparagin may be used as a 

 further test ; the precipitated crystals will not dissolve 

 in it, but will be dissolved on the addition of water. 



In performing these tests it is better to use longitudinal than 

 transverse sections. 



C. The Micro-physics of the Cell. 



I. Imbibition. 



This term is used to express the fact that the 

 cell-wall and certain of the cell-contents (proto- 

 plasm, starch-grains, aleurone-grains, crystalloids) 

 usually contain a certain amount of water, termed the 

 water of imbibition. The amount of water of imbi- 

 bition may be made to vary by appropriate re-agents, 

 and this involves variation in size of the body observed. 

 These phenomena are best seen in cell-walls and in 

 starch-grains ; the cell-walls should be such as are 

 thickened, and consist of cellulose; those which are 

 chemically altered (either cuticularised or lignified) 

 cannot be made to vary to any considerable extent. 



Cut a transverse section of the petiole of the Sun- 

 flower (Elder or Mallow will do as well) ; mount in 

 water ; examine with high power. 



Observe just beneath the epidermis, several layers of 

 cortical cells, the walls of which are thickened at their 

 point of junction (collenchyma). 



Bun in some potash solution, or some moderately 



