CELL-CONTENTS AND FORMS OF CELLS. 231 



a fine net- work, as in Fig. 125, D, E. (3) A third type in which 

 the secretion is in the form of neither rods nor vacuoles but a 

 somewhat cellular structure, termed by Tunmann a lattice-work. 

 In the walls of the glandular hairs other substances are some- 

 times present, as resins, gums, etc. Hanstein originally pro- 

 posed the use of a mixture of aniline dyes to distinguish resin, 

 gum, and protoplasm (Bot. Zeit., 1868, p. 754), but later studies 

 have shown that these dyes are limited in differential diagnosis 

 of many of these substances. The cells of the glandular hairs 

 may contain, in addition to protoplasm, protein bodies, chloro- 

 phyll grains, starch, fixed oil, tannin, calcium oxalate, reducing 

 sugars, and other special substances, which are colored yellowish- 

 red with solutions of the alkalies or sulphuric acid. 



MlCROCHEMISTRY OF THE VOLATILE OlLS AND RESINS. They 



are readily soluble in alcohol, .ether, chloroform, benzene, acetic 

 ether, carbon disulphide, petroleum ether, etc. They are also 

 quite soluble in glacial acetic acid and in aqueous solutions of 

 hydrated chloral. Some of them are soluble in dilute alcohol. 

 They may be liberated on the heating of sections for about ten 

 minutes in a drying oven to a temperature between 100 and 

 130 C. Like the fixed oils, they are colored brownish or 

 brownish-black with osmic acid and are intensely colored with 

 alkannin and cyanin. The volatile oils are also colored a carmine 

 red with very dilute solutions of fuchsin. Cells containing resins 

 and terpenes are colored green by the use of aqueous solutions 

 of copper acetate, the freshly cut twigs or leaves being allowed 

 to remain in the solution for a few days. 



VOLATILE OILS. The odors which are characteristic of 

 very many plants are due chiefly to a group of principles known 

 as volatile oils. They are, for the most part, mixtures of terpenes 

 and camphors, and are obtained from the plant by distillation 

 with steam, the oil rising to the surface of the distillate, being 

 only slightly soluble in water. Volatile oils are readily soluble 

 in alcohol, ether, chloroform, and in the fixed oils. Some of 

 them show a tendency to absorb oxygen, and are converted into 

 resinous substances. They are widely distributed and are char- 

 acteristic of certain families, viz. : Pinacese, Cruciferse, Labiatae, 

 Lauracese, Myrtaceae, Rutacese, and Umbelliferae. 



