24 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



E. Oil. Oils may be recognized by tlieir characteristic appearance as seen 

 in minute droplets in the tissues of the plant when examined with the 

 microscope. Thin sections containing oil, when treated with ether or 

 chloroform, lose the oil almost instantly. Oils (and resins also) are 

 colored a deep red by the alcoholic solution of alkannin (Sec. 170) or of 

 the soluble material in alkanet root. Make the test on a thin section of 

 an oily seed (not Eicinus seed) placed under the microscope in an 

 alcoholic solution of alkannin. 



F. Proteids. Proteids usually give a brick-red or rose-red color when 

 moistened with Millon's reagent (Sec. 170) and gently heated. They 

 are stained yellow or brown by iodine solution. All proteids turn 

 yellow (xanthoproteic reaction) when moistened with strong nitric acid 

 and slightly warmed. The color deepens on the addition of ammonia 

 water to the stained substance. To make the nitric-acid test, warm a 

 little egg albumen with the strong acid, and when the coagulated 

 albumen becomes decidedly yellow pour off the excess of acid and 

 cover the stained mass with a little ammonia water. 



Eefekenoes. For the substances to be tested. Principles; Pfefler, 31 ; for 

 the tests themselves, Zimmerman's Botanical Microtechnique (Henry 

 Holt & Co., New York), and Strasburger-Hillhouse, 6. 



EXPERIMENT VII 



Occurrence of starch in seeds. Cut in two with a sharp knife the 

 seeds to be experimented on, and then pour on each, drop by 

 drop, some iodine solution. Only a little is necessary ; sometimes 

 the first drop is enough. 



If starch is present a blue color (sometimes almost black) will 

 appear. If no color is obtained in this way, boil the pulverized 

 seeds for a moment in a few drops of water and try again. 



Test in this manner corn, wheat (in the shape of flour), oats 

 (in oatmeal), barley, rice, buckwheat, flax, rye, sunflower, four- 

 o'clock, morning-glory, mustard seed (not ground mustard), beans, 

 peanuts, Brazil nuts, hazelnuts, and any other seeds that you can 

 get. Eeport results in tabular form. 



Eefekenoe. Strasburger-Hillhouse, 6. 



13. Absorption of starch from the cotyledons. Examine with the micro- 

 scope, using m.p. (medium power), thin sections of soaked beans and the 



