ABSORPTION OF CARBON 



15 



'sixties of last century, observed the formation of starch in the 

 cells of Spirogyra, 30 min. after the beginning of the experiment. 

 A convenient method for detecting the accumulation of starch 

 is the well-known Sachs test. A leaf, having been exposed to 

 light, is decolorized by means of alcohol and afterwards treated 

 with iodine solution. If separate areas of the leaf are shaded, 

 prior to the experiment, with opaque paper, there will be produced 

 light figures on the general dark background of the leaf. The 

 relationship between the amount of transmitted light and the 

 accumulation of starch is so close that by means of this method it 



Die. 6. — Prints from negatives on leaves made by means of a starch test (from 



Molisch) . 



is possible even to print on the leaves portraits from negatives 

 just as on a sensitive paper (Fig. 6). 



Starch is the most easily detectable product of assimilation. 

 This does not mean, of course, that it is the first product, for it 

 represents a too complicated structure made up of very large 

 molecules. Its formation in the leaf is preceded by different 

 kinds of sugars. Exact quantitative determinations show that 

 not over 30 to 50 per cent of the products of assimilation is 

 deposited in the form of starch, the rest being sugars. In many 

 plants, for instance the onion, tulip, Arum, etc., the process of 

 assimilation terminates with the formation of sugars. Such 

 plants are called "saccharophilous," in distinction from the usual 

 "amylophilous ones," i.e., plants accumulating starch. The 

 accumulation of starch must be regarded as a secondary process, 

 the purpose of which is to withdraw as soon as possible the soluble 



