BOTANICAL MICROTECHNIQUE. 



cover-glass, places at the edge of the latter a drop of sul- 

 phuric acid, and warms the whole until it steams, for not 

 over a minute. By pressure on the cover-glass a complete 

 isolation of the separate cells may be accomplished, and any 

 starch present, not being dissolved by the sulphuric acid 

 diluted with glycerine, becomes readily visible by being 

 colored by the iodine. In the case of soft parts of plants, 

 leaves and herbaceous stems, this method may do excellent 

 service. But for wood and the like I have not found it 

 suited. 



IV. Swelling. 



10. Especially to bring out better certain structural rela- 

 tions of membranes and starch-grains, there may sometimes 

 be used the so-called swelling media, which produce an 

 increase of volume depending chiefly on increased water- 

 content. 



The most used medium is aqueous caustic potash, which 

 causes a greater or less swelling according to its concentra- 

 tion. It is, moreover, very well adapted for the study of 

 the swelling phenomena of protein crystalloids. 



Concentrated sulphuric acid is also a strong swelling 

 medium, and finally quite dissolves membranes consisting 

 of pure cellulose. Cuprammonia (cf. 246) acts similarly. 



As a swelling medium for starch-grains chromic acid has 

 been frequently recommended. 



Finally, Dippel (I) used a solution of mercuric iodide in a 

 potassium iodide solution for making clear certain membrane 

 structures. The proper concentration of this solution must 

 be determined for each special case. 



V. Clearing. 



11. In many cases, where one wishes not so much to study 

 the entire contents of various cells as to determine their 

 general arrangement, the courses of vascular bundles, or the 

 distribution of less soluble cell-contents, as, for example, 

 calcium oxalate crystals or similar bodies, it may be desira- 



