7O THE MICROSCOPICAL NEWS. 
Resins.—When examining the oleo-resinous ducts of plants, 
especially in the Conifer, Cycadez, Aroidez, Umbelliferze, Arali- 
acez, Composite, and Clusiaceze, in which they are very much 
developed, we must eliminate the resins which accumulate in the 
passages where they were originally united with the essential oils, 
as has been done by Sachs,* Trécul,t N. J. G. Miiller,t and Ph. 
van Tieghem.§ It is the same with the vesczs properly so called 
(betulin, colophane, jalap, lac, &c.), the da/sams (tolu, benzoin, 
&c.), the gum-resins (gamboge, &c.). These substances, abundant 
in the sections of old tissues, generally prevent the study of the 
oleaginous cells. They can be completely dissolved in the fixed 
oils by heat. But it is generally preferable to treat them with 
essential oils, ether, or alcohol, which at ordinary temperatures 
dissolve the greater portion of them. The little which remains in 
the passages does not injure the examination of the preparation, and 
moreover this imperfect solution of the resin, joined to its other 
characters, helps in its recognition. 
Waxy matters.—The waxy matters of the cuticles are but slightly 
soluble in cold alcohol, but they dissolve very quickly in boiling 
alcohol or slightly warmed ether. It is the sections themselves which 
are subjected to the action of these liquids in order to obtain per- 
fectly pure cuticles, or to recognize the waxy nature of the sub- 
stances developed at the surface of these membranes. 
Latex.—In making sections of organs provided with latex, care 
must be taken to keep the razor and the preparations continually 
wet with ether. Without this precaution the latex blackens the 
razor, and consequently the tissues which are being cut, so that it 
becomes impossible to examine them. 
Caoutchouc is composed of the corpuscles of the latex of certain 
plants. These corpuscles can be recognized under the Microscope 
by their swelling in the volatile oils, and dissolving in benzene, 
chloroform, and bisulphide of carbon. 
Cellulose.—Cellulose, as it is most frequently present in the 
cells, that is in the condition of polymerization not exceeding 
(C,H O0;)4, is soluble in Schweitzer’s ammonio-cupric solution. 
More condensed (for instance, elder pith, the walls of thickened 
fibres, old vessels, ligneous cells) it is insoluble in the same reagent. 
Schweitzer’s solution alters with time, therefore it ought to be 
used freshly prepared. It is obtained by pouring ammonia on 
copper turnings, in a funnel ; the liquid is again poured over the 
copper until it is coloured deep blue. 
* Bot. Ztg., 1859, pp. 177-85. 
+ Journ. de l'Institut, 6th Aug., 1862. Ann. Sci. Nat., v. and vii. 
+ ‘ Untersuchungen iiber die Vertheilung der Holze,’ 1867. 
§ ‘ Mém. sur les canaux sécréteurs des plantes,” Ann. Sci. Nat., xvi. (1872). 
