80 
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 are 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 iso¬ 
lation 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 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- 
monia can be prepared by pouring 15 per cent ammonia water upon 
copper turnings or filings. Let the solution stand in an open bottle. 
It does not keep well, but its efficiency is readily tested. Cotton 
dissolves almost immediately as long as the solution is fit for use. 
