320 PLANT AND ORGANIC CHEMISTRY 



row, 1 by the action of lime-water on oxymethylene, in the form 

 of a syrupy liquid which he named methylenitan. In 1863, 

 Van Deen, by the oxidation of glycerine, discovered a com- 

 pound which reduced salts of copper in alkaline solution, and 

 showed other properties indicative of a sugar, although of a 

 simpler kind than those found in nature. The discoveries of 

 Low, Tollens, and Fischer have brought the investigations of 

 sugars to our own times. 



The researches of Nageli, from a botanical standpoint, 

 led him to advance a theory that starch was the origin of sugar 

 in plants. 



A later purely chemical hypothesis of the synthesis of sugars 

 from simple compounds in the living cell, which, in turn, yield 

 more complicated compounds, is thought by many to be a 

 more satisfactory theory, for it coincides with our ideas de- 

 rived from other branches of scientific investigation, in sup- 

 port of the notion that from simple integrals arise intricate 

 structures. But it is quite probable that both processes of con- 

 struction and destruction are carried on simultaneously in the 

 plant. In the laboratory it is possible, starting with the ele- 

 ments carbon, hydrogen, and oxygen, to form, from these ele- 

 ments, compounds which are found in vegetable life. From 

 the simple bodies thus derived are the means ready at hand 

 to proceed to compounds of a sugar type. 



The carbon dioxide in the plant is derived from the exter- 

 nal environment of the air and soil, or the gas is generated 

 within the plant cells. Under the influence of sunlight, car- 

 bon dioxide and water yield formaldehyde, a compound con- 

 taining the group (CHO); i. e., one atom respectively of 

 carbon, hydrogen, and oxygen, known as the aldehyde group, 

 united to hydrogen by the residual affinity of carbon. Accord- 

 ing to Baeyer, formaldehyde is the source of the plant's sugar. 



In the chlorophyll grains of the green part of the leaf, it is 

 supposed that the formation of glucose takes place. 



The aldehyde group enters into the constitution, and is 

 characteristic, of many of the sugars. One of the divisions in 

 the classification of sugars containing this group is known as 



1 Ann., cxx, 295. 



