750 SUMMARY OF CUERENT KESEAECHES RELATING TO 



solubility and density of several essential oils, whicli it is useful to 

 know, in order to free the sections from them. 



A. Essential oils denser than water : — Bitter almonds, cloves, 

 mustard, cinnamon. 



B. Essential oils less dense than water : — 

 Camphor. 



Essence of roses, soluble in suljjhuric acid. 



Essential oil of aniseed : when sulphuric acid is added to it in 

 sufficient quantity, the solution separates into two layers, of which 

 only one is fluid. 



Essential oils of conifers, only soluble in several times their 

 volume of alcohol. 



Essential oil of lavender, soluble in one volume of alcohol. 



Essential oil of rosemary, mint, and thyme, very soluble in 

 alcohol. 



Bcsins. — When examining the oleo-resiuous ducts of plants, 

 especially in the Couiferge, Cycadese, Aroidea), Umbelliferae, Arali- 

 acc8B, ('ompcsitfe, and Clusiaccfe, 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,* Trecul,! N. J. G. ]V[uller,J and Ph. van 

 Tieghem.§ It is the same with the resins properly so called (betulin, 

 colophane, jalap, lac, &c.), the balsams (tolu, benzoin, &c.), the gum- 

 resins (gamboge, &c.). These substances, abundant in the sections of 

 old tissues, generally prove nt the study of the oleaginous cells. They 

 can be completely dissolved in the fixed oils by heat. But it is gene- 

 rally 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 examina- 

 tion of the preparation, and moreover this imperfect solution of the 

 resin, joined to its other characters, helps in its recognition. 



Waxy matUrs. — 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 perfectly jjure cuticles, or to recognize the waxy nature of 

 the substances developed at the surface of these membranes. 



Latex. — In making sections of organs j^rovided 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 couipc sed of the corpuscles of the latex of certain 

 plants. These corpuscles can be recognized under the Microscoije by 

 their swelling in the volatile oils, and dissolving in benzin, chloro- 

 form, and bisulphide of carbon. 



* I3ot. Ztj-;., 1859, pp. 177-85. 



t Jouin. do ritistitut, 6tli Aup:., 1862. Ann. Sci. Nat., v. and vii. 



j ' Uutersuchungcu iiber die Vcrtheilung dor Holze,' 18G7. 



§ " Mem. sur ius cauaux se'cre'teurd dcs plautes," Ann. Sci. Nat., xvi. (1872). 



