210 A TEXT-BOOK OF BOTANY. 



may be either colorless or of an intensely yellow or bright red 

 color, giving a distinct reaction for tannin. The cell-sap is soluble 

 in water and in alcohol and gives an acid reaction. In the yellow 

 idioblasts upon treatment with nitric acid it is colored orange-red, 

 changing to reddish-brown ; with concentrated sulphuric acid it 

 becomes orange-red and finally of a rose-red or crimson 

 color; with solutions of the alkalies it becomes greenish, and it is 

 precipitated with solutions of potassium bichromate, ferric acetate, 

 or ferrous sulphate, the precipitates resembling those found with 

 tannin. Zopf found that the tannin idioblasts may possess either 

 a colorless content or, in addition, have a yellow coloring prin- 

 ciple (yellow anthocyanin) or a red pigment (red anthocyanin). 

 He considers that the yellow pigment is derived from a colorless 

 chromogen and that the red pigment may be formed from either 

 a colorless chromogen or from yellow anthocyanin. Further- 

 more, he concludes that there is a relationship in the Fumariaceae 

 between the anthocyanin and tannin, as the two constituents are 

 always found in the same cell. It is rather interesting to note 

 that chloroplasts may be found in the idioblasts, and that sugar 

 is also a constituent in the idioblasts, occurring in the young roots 

 and stems of Diclytra spectabilis. 



Tannin idioblasts are found in the palisade tissues of leaves 

 or in the parenchyma cells of roots and stems of some of the 

 genera in the Geraniacese, Celastraceae, Rhamnaceae, Legumi- 

 nosae, Solanaceae, Rubiaceae, Scrophulariaceae, Polygonaceae, 

 Aristolochiaceae, Piperaceae, Euphorbiaceae and Moraceae. 



THE FIXED OILS, FATS, AND WAXES include a group of sub- 

 stances whiclj are widely distributed in plants, occurring especially 

 abundant in seeds, fruits, and barks. They are distinguished by 

 the fact that in their chemical constitution they possess radicals 

 of the fatty acids. In the diatoms, Vaucheria, and some of the 

 other lower plants fixed oils arise in the chromatophores in place 

 of starch, thus being the first visible product of photosynthesis. 

 Fixed oils usually occur in reserve cells as in seeds and the 

 parenchyma and medullary ray cells of roots and rhizomes. They 

 are either found in the vacuoles of the protoplasm or are formed 

 in the cell-wall, and usually are liberated in the form of globules 

 upon healing the sections or treating them with solutions of 



