STARCH: TRANSLOCATION. 75 



tion as in water, are called carbohydrates. The most common carbo- 

 hydrates are sugars (cane sugar, C 12 H 22 O n , for example, in beet roots, 

 sugar cane, sugar maple, etc.), starch, and cellulose. 



155. Vaucheria. The result of carbon dioxide assimilation in the 

 threads of Vaucheria is not clearly understood. Starch is absent or diffi- 

 cult to find in all except a few species, while oil globules are present in 

 most species. These oil globules are spherical, colorless, globose and 

 highly refringent. Often small ones are seen lying against chlorophyll 

 bodies. Oil is a hydrocarbon (containing C, H, and O, but the H and O 

 are in different proportions from what they are in H 2 O) and until recently 

 it was supposed that this oil in Vaucheria was the direct result of photo- 

 synthesis. But the oil does not disappear when the plant is kept for a 

 long time in the dark, which seems to show that it is not the direct prod- 

 uct of carbon dioxide assimilation, and indicates that it comes either from 

 a temporary starch body or from glucose. Schimper found glucose in sev- 

 eral species of Vaucheria, and Waltz says that some starch is present in 

 Vaucheria sericea, while in V. tuberosa starch is abundant and replaces the 

 oil. To test for oil bodies in Vaucheria treat the threads with weak osmic 

 acid, or allow them to stand for twenty-four hours in Fleming's solution 

 (which contains osmic acid). Mount some threads and examine with 

 microscope. The oil globules are stained black. 



2. Sugar, and Digestion of Starch.* 



156. The sugar produced as the result of photosynthesis may be stored 

 as sugar or changed to starch. In general sugar is more common in the 

 green parts of monocotyledonous plants, while starch is most frequent in 

 dicotyledons. Plant sugars are of three general kinds : cane sugar or sucrose, 

 abundant in the sugar cane, sugar beet, sugar maple, etc.; glucose or 

 fruit sugar, found in the fruit of a majority of plants, and abundant in some, 

 as in apples, pears, grapes, etc. (in many fruits and other parts of plants 

 both glucose and cane sugar are present); and maltose, as in malted barley. 



157a. Test for sugars. Make a weak solution of pure commercial 

 grape sugar (glucose) and also one of pure granulated cane sugar. Partly 

 fill two test tubes with Fehling's solution. f To one add some of the grape- 

 sugar solution and to the other add some of the cane-sugar solution. After 

 these tubes have stood in a warm place a few hours, it will be found that 

 a bright orange-brown or cinnabar-colored precipitate of copper and cuprous 

 oxide has formed in the tube containing grape sugar, while the other solu- 

 tion is unchanged. Grape sugar or glucose therefore reduces Fehling's 

 solution, while cane sugar as such has no effect upon it. 



1576. Test for cane sugar. Place a small quantity of pure granulated 

 cane sugar in a test tube and add about 15 cc. of distilled water. To 



* Paragraphs 156-160 were prepared by Dr. E. J. Durand. 



* See page 712 for formula for Fehling's solution. 



