THE FIKST VISIBLE PRODUCT. 321 



is apparent at a glance. The raw materials, the apparatus, 

 and the ultimate products of manufacture are known ; but the 

 intermediate processes b}- which chloroph} 11 granules under the 

 influence of certain rays of light can cause the dissociation of 

 carbon from the oxj-gen with wliicli it is combined in carbonic 

 acid, and bring about the sj'nthcsis of an organic substance from 

 materials wholly inorganic, are not at present known. 



845. The wide field which the synthesis of organic from inor- 

 ganic matter opens to conjecture has not been left unoccupied. 

 It is generally admitted that in assimilation there is first formed 

 some ternary substance, namely, one which contains the three 

 elements, carbon, h3'drogen, and oxjgen ; and further, that 

 this contains less ox^-gen than the two inorganic matters, car- 

 bonic acid and water, from whicli it is produced, taken to- 

 gether. Exactly what the ternary substance is, or how the 

 dissociation or reduction is carried on in the chloroph3ll granule, 

 is still left in doubt. 



846. Starch (CjII^O^) is the first visible product of assimila- 

 tion, as was first pointed out by Sachs in 1862.* Although 

 Sachs appears to have held at one time that it is the first pro- 

 duct, his later expressions are more guarded, and simply state 

 the fact universally admitted, namel3-, that starch is the first 

 product which the microscope can detect. When a seedling has 

 been kept for a time in a diml^- lighted room, its cotyledons and 

 other leaves grow pale or etiolated, and if they are examined 

 for starch, no trace of it will be found. But upon a very short 

 exposure of the plant to the direct raj-s of the sun, provided the 

 other conditions are favorable, a certain amount of starch will 

 appear in the chlorophj-U granules of the cells at the margin of 

 the leaves. If the plant is again withdrawn from the light, its 

 scant}' store of starch is speedily consumed, but on renewed in- 

 solation the loss is made good ; this process can be repeated 

 many times. From the constant appearance of starch in the 

 chlorophj'U granules under the above circumstances it has been 

 generally recognized as the first visible product of assimilation 

 proper. But it has obviously such a complex molecular struc- 

 ture that chemists are unwilling to believe that its formation in 

 the plant is not preceded b}- the production of some simpler 

 substance. Furthermore, there are a few cases in which oil 

 replaces starch as the first visible product, thus indicating that 

 there may be some earlier product possibly' common to both. 



1 Botanische Zeitung, 1862 ; Flora, 1862. 

 21 



