LIFE AND LIGHT 27 



obtained. All this does not demonstrate that the first action of the 

 chloroplastid is identical in kind, and, moreover, it furnishes no 

 light whatever on the role played by the plastid or the chlorophyll 

 it contains. It merely leaves the chloroplastid out, so to speak ; 

 but in some way or other the carbon dioxide and water molecules 

 must at some stage in the synthesis have chemical attachment to 

 either the chlorophyll or colourless matter of the plastid, and this 

 attachment must be of an unstable vibratile type, which can be 

 influenced by the vibrations of the light waves. When once the 

 carbon dioxide and water molecules become attached to the colloidal, 

 organic complex molecules of the plastid, they become reduced by 

 the agency of the light waves which yield energy for the detachment 

 of the oxygen, and the conversion thereby of the newly attached 

 groups to the big molecule, as aldehydic, carboxylic, or ketonic 

 groups, or it may be as amidogen groups if simple nitrogenous in- 

 organic groups are simultaneously presented. These new groups 

 are attached very similarly to polypeptide formation, or like the 

 process of manufacturing the long chain of the fatty acid, or like 

 the acids of so many glucosides found in plant structures. There is 

 no necessity experimentally or theoretically to suppose that they 

 should always be detached from the synthesising mechanism of the 

 plastid as free formaldehyde, nor to suppose that formaldehyde as 

 such is formed anywhere along the line. The next process, when 

 these have become too abundant or condensed in connection with 

 any colloidal molecule in the plastid, will be the shedding of them off 

 as reserve material in the form of starch granules or fatty droplets. 1 

 This view would bring starch production in photo- synthesis into line 

 with known metabolic processes going on in other organs of the 

 plant, such as roots, tubers, and seeds, where from sugar brought 

 from leaves or elsewhere are formed starchy, fatty, or protein 

 depots as also with the facts of animal metabolism, where ingested 

 sugar in excess of immediate demands is stored as glycogen, or as 



1 The hexoses are always active bodies on account of the presence of the 

 aldehydic or ketonic group ; in the formation of higher carbohydrate, or of fats, 

 these groups either disappear on account of molecular changes, or neutralise 

 each other by interlinking, so that quite neutral bodies tend to form as the 

 molecule becomes more complex. From this point of view it is interesting 

 to point out that sucrose, or cane-sugar, which consists of two very active 

 hexoses viz., glucose and fructose loses its active properties, and no longer 

 acts as a reducing agent from the interlinking of the aldehydic group of the 

 glucose with the ketonic group of the fructose. 



