908 EXPERIMENT STATION RECORD. 



readily yield a sugar containing five molecules of formic aldehyde, and 

 persite, found in the fruit of the alligator pear, which contains seven 

 molecules of the aldehyde. 



Starch is easily transformed into glucose by simply heating the starch 

 with weak acid solution. This in fact is the method employed in the 

 commercial preparation of glucose. Starch is also transformed into 

 glucose during germination by the action of a ferment present in the 

 seed. This change is so easy and so frequent that there is no doubt 

 that the transformation could be reversed; that is, the glucose could be 

 changed into starch. Up to the present time, however, this has not 

 been done by purely chemical means, but when leaves are placed in a 

 solution of glucose starch soon appears in them. The starch is formed 

 from the glucose through the combination of several molecules of the 

 latter, water being eliminated. 



Starch is very abundant in leaves which have been exposed to sun- 

 light. Its presence is more easily detected than that of glucose. The 

 latter is but a transition stage, while the starch is reserve material 

 which remains in the tissues much longer than glucose. 



The starch which is so abundant at the end of the day disappears 

 during the night. The leaf is thus seen to be both a laboratory and a 

 storehouse which is continually emptying and tilling itself. The starch 

 disappears from the leaves in the form of glucose. Adult plants utilize 

 this transfer form of starch in the formation of cellulose, just as young 

 plantlets utilize the glucose formed from starch in the cotyledons of the 

 seed during germination. 



The different steps have now been traced in the formation of the 

 organic matter of plants from the simple carbon dioxid absorbed to the 

 complex carbohydrates of the plant tissues. It now only remains to 

 briefly discuss the derivation of some particular forms of these carbo- 

 hydrates. Among the most important of these is cellulose, which 

 forms the envelope of the cells and which is easily changed into reduc- 

 ing sugars under the action of acids. It appears during the germina- 

 tion of seeds simultaneously with the disappearance of starch. There 

 is little doubt that it is derived from glucose and consequently from 

 formic aldehyde. It seems clear, therefore, that all the carbohydrates, 

 the gums, sugars, starch, inulin, and cellulose originate in the activity 

 of the chlorophyll cells. The same is probably true of the tannin 

 and resin groups. There are, however, certain plants which contain a 

 group of sugars known as the inosites which are true carbohydrates, 

 but whose molecular construction is different from that of the other 

 glucoses, since their derivatives belong to the aromatic series and not 

 to the fatty acid series to which the other groups belong. 



There is one other important point which needs some explanation. If 

 we study the X)henomena of assimilation in a leaf which has been 

 exposed to sunlight, we will find that the volume of oxygen evolved 

 equals that of the carbonic acid decomposed. The plant utilizes the 



