THE CHLOKOPHYLL APPAKATUS 153 



appears to be the first carbohydrate to be formed ; it is not 

 very readily detected, being freely soluble in the cell-sap. 

 Almost as quickly as the formation of sugar we have the 

 appearance of starch in the substance of the chloroplasts, 

 and as this is easily visible, it was long thought that starch 

 was the culminating product of the photosynthetic process. 

 We shall find reasons shortly for suggesting a wholly different 

 meaning to the appearance of the starch, that it is indeed 

 only a temporary store of carbohydrate in an insoluble 

 condition, due to the production of sugar being in excess 

 of the quantity needed by the cell for immediate consump- 

 tion. 



If we accept the view of the polymerisation of formalde- 

 hyde to give rise to the sugar, we cannot withdraw this 

 operation also from the activity of the chloroplast. Sugars 

 are what are called optically active compounds : that is, they 

 possess the power of deflecting a ray of polarised light to 

 the right or to the left as the latter is made to pass through 

 either crystals or a solution of them. Formaldehyde has no 

 such power. There is no process known by which an 

 optically active compound is formed from an optically 

 inactive one without the intervention of living substance. 

 Consequently we must suppose that the polymerisation is 

 brought about by the chloroplast as certainly as is the 

 original change of the carbon dioxide. 



We have so far assumed that a sugar having the 

 formula C 6 H 12 6 , and known as a hexose, is the first carbo- 

 hydrate formed. This, however, is not certain. Some ex- 

 periments carried out in 1892 by Brown and Morris point 

 rather to cane-sugar as the first carbohydrate synthesised. 

 Cane-sugar is a more complex substance, and has the formula 

 C 12 H 22 O lr This conclusion is based on repeated observations 

 that when leaves of Tropceolum were plucked and then ex- 

 posed to sunlight for twelve hours, there was a great accu- 

 mulation of this sugar in the leaf, while the simpler hexoses 

 did not increase in quantity. The severance of the leaves 

 from their stems prevented the transport of the sugars to 



