84 METHODS IN PLANT HISTOLOGY 



When proteins are heated with Millon's reagent, the solution be- 

 comes brick-red or rose-red. This reaction takes place slowly even in 

 the cold. The following is one formula for this reagent: 



Mercury 1 c.c. 



Concentrated nitric acid 9 c.c. 



Water 10 c.c. 



Dissolve the mercury in the nitric acid and add the water. 



Fats and oils. — The fatty oils are not soluble in water and are only 

 shghtly soluble in ordinary alcohol. They dissolve readily in chloro- 

 form, ether, carbon disulphide, or methyl alcohol. 



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

 cause ethereal oils and resins take the same red color. Dissolve com- 

 mercial 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, and the black remains even after all the processes of the paraffin 

 method. The black can be bleached out in hydrogen peroxide, or 

 chlorine (see p. 27). 



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 mid- 

 dle lamella are none too well known; its microchemistry has pro- 

 gressed 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 intercellular spaces 

 arise through the natural solution or gelatinization of the lamella. 



In polarized light, with crossed Nicols, the middle lamella is resolved 

 into three lamellae, the middle one appearing dark, and the two outer 

 lamellae, hght. 



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. 



