RECOGNITION OF SUBSTANCES IN PLANTS 23 



the dirty white portion, of cheesy consistency, embryo; and 

 the yellow portions, and those which are white and floury, 

 endosperm. 

 D. Chip off the endosperm front one kernel so as to remove 

 the embryo free from other parts. Notice its form, some- 

 what triangular in outline, sometimes nearly the shape of 

 a beechnut, and in other specimens nearly like an almond. 

 Estimate what proportion of the entire bulk of the soaked 

 kernel is embryo (Principles, Fig. 378). Split the embryo 

 lengthwise so as to show the slender plumule. 



13. Recognition of some chemical compounds found in plants.* * Out of the 

 very numerous substances which make up the framework of the plant body, 

 or are stored in it, there are several most important ones which the student 

 should be able to recognize by simple tests. In this place only starch, sugar, 

 cellulose, lignin, oil, and proteids will be discussed. 



A. Starch. This turns blue, or nearly black, on the addition of iodine 

 solution. Make the test on a bit of laundry starch the size of a grain 

 of wheat diffused in a large test tube full of boiling water ; it does not 

 form a true solution. Add the iodine solution (Sec. 169) drop by drop 

 to the boiled starch after the latter has cooled. 



B. Sugar. Some of the sugars found in plants produce a yellow or orange 

 color or an orange precipitate on'being heated to boiling with a solution 

 of copper known as Fehling's solution (Sec. 170). Cane sugar does not 

 give the reaction readily unless it has first been boiled with dilute 

 hydrochloric acid, when it responds promptly to the test. Make the 

 test with Fehling's solution on a rather dilute solution of commercial 

 glucose in hot water. 



C. Cellulose. This turns blue on being moistened with iodine solution 

 and then with concentrated sulphuric acid diluted with half its hulk 

 of water. Make the test with a bit of absorbent cotton (in this par- 

 ticular case wetting the cotton first with the acid and then with the 

 iodine solution). 



D. Lignin. This substance, which forms a large part of the material of 

 lignified cell walls, gives a reddish violet color with phloroglucin solution 

 (Sec. 170) after the addition of hydrochloric acid. Make the test by 

 moistening a thin shaving of any kind of light-colored wood with a 

 solution of as much phloroglucin as can be taken up on the point of a 

 penknife in thirty or forty drops of 95 per cent alcohol. Then wet the 

 moistened shaving with a little concentrated hydrochloric acid. 



