76 Methods in Plant Histology 



Fats and Oils.- -The fatty oils are not soluble in water and are 

 only slightly soluble in ordinary alcohol. They dissolve readily in 

 chloroform, ether, carbon disulphide, or methyl alcohol. 



Alcannin colors oils and fats deep red. The test is not decisive, 

 because ethereal oils and resins take the same red color. Dissolve 

 commercial alcannin in absolute alcohol, add an equal volume of 

 water, and filter. The fats and oils in sections left in this solution 

 for 24 hours should be bright red. The reaction is hastened by 

 gentle heating. 



Osmic acid, as used in fixing agents, colors fats and oils brown 

 or black. The dark color is removed by bleaching in a 3 to 10 per 

 cent solution of hydrogen peroxide. 



In case of fats and oils, solubility and color reactions are useful, 

 but must be regarded as corroborative evidence, not as decisive 

 proof. For more critical and detailed methods, consult the book by 

 Tunmann, which will also give the literature of the subject. 



The Middle Lamella. Even the origin and development of the 

 middle lamella is none too well known; its microchemistry has 

 progressed but little beyond the color-reaction stage. The middle 

 lamella consists largely of pectin or pectic compounds. The easy 

 isolation of cells, when treated with Schultze's maceration, depends 

 upon the ready solubility of pectins in this reagent. Many inter- 

 cellular spaces arise through the natural solution or gelatinization 

 of the lamella. 



In polarized light, with crossed Nichols, the middle lamella is 

 resolved into three lamellae, the middle one appearing dark, and 

 the two outer lamellae, light. 



Ruthenium red is a good stain, since it gives as good results as 

 any and has the advantage of keeping well in balsam or glycerin 

 jelly. Make a very weak solution 1 g. to 5,000 c.c. of water, 

 or even weaker and keep it in the dark. It stains many other 

 things besides the lamella, but is, nevertheless, a good stain. 



Pectin is not at all confined to the middle lamella, but is found 

 in other membranes, particularly in spore coats. 



Cellulose. In concentrated sulphuric acid cellulose swells and 

 finally dissolves. It is also soluble in cuprammonia. The cupram- 



