THE PRODUCTS OF PHOTOSYNTHESIS 201 



acid has been used as a test for this group of sugars. Levulinic acid 

 forms a crystallizable silver salt which has been used for its identification.^* 



A specific reaction for ketoses has been described by Pinoff ; ^^ this 

 is a modification of the familiar Molisch reaction. About 50 mg. of the 

 sugar to be tested with 10 cc. alcoholic sulfuric acid (75 cc. + 20 cc.) and 

 0.2 cc. of a 5 per cent alcoholic solution of alpha-naphthol are heated in a 

 water-bath to 95-98°. In the presence of a ketose the solution becomes 

 violet within one minute and should not be heated more than three minutes. 

 With longer heating the aldoses also develop a faint violet color which 

 increases with time. 



The Seliwanoff ^^ reaction for ketoses takes advantage of the fact that 

 ketoses form 4-oxymethyl furfural more readily than the aldoses. About 

 50 cc. of the sugar solution with 10 cc. normal hydrochloric acid and 10 

 mg. resorcinol are heated in the boiling water bath for 15 minutes. In 

 the presence of ketoses a red coloration is produced. As pentoses, and 

 more slowly also aldoses produce a color the reaction cannot always be 

 relied upon for keto-hexoses. 



d-Glucose is probably the most widely distributed organic compound 

 in plants. At some time in their development it is found in almost all 

 plant parts and while the amounts present vary considerably with the sea- 

 son and external conditions, it is highly probable that glucose is present, if 

 only in traces. Which one of the sugars is the first to appear in the photo- 

 synthetic process we shall discuss in a later portion of this chapter. 

 Suffice it for the present that most evidence points to the conclusion that 

 carbohydrates are the first products which accumulate in the photosynthetic 

 activity of chlorophyllous cells. The products of photosynthesis are stored 

 in the plant as condensation products of glucose in one form or another, 

 namely, sucrose, dextrine, starch and cellulose. But the movement of 

 the material from one part of the plant to another, as from the leaves to 

 the roots, usually takes place in the form of the simpler carbohydrates, 

 the products of hydrolysis of the storage material, and of these, glucose 

 is a common form. 



All living things require a continuous supply of energy for maintaining 

 their activity. A majority of living organisms obtain this energy from 

 the chemical transformations which the carbohydrates are capable of under- 

 going, and in this function glucose plays a very important role. In the 

 higher plants the carbohydrates are usually in this process converted to 

 carbon dioxide and water by oxidation, with the occasional formation of 

 hydroxyacids. Lower organisms, fungi and bacteria, on the other hand, 

 produce a variety of products such as alcohols, lactic, succinic and citric 

 acids. Throughout almost the entire plant and animal kingdoms glucose 

 is a most valuable food. The chemical changes which glucose undergoes 



"Wehmer and ToUens, Bcr. clwm. Ges.. 33, 1286 (1900). Levene, Zeit physiol 

 Chan., 43. 199 (1904-1905). 



"Pinoff, Bcr. chcm. Ges., 38, 3308 (1905). 



"Seliwanoff, Ber. chcm. Ges., 20, 181 (1887). Konigsfeld, Biochem. Zeit 38 

 310 (1912). ' ' 



