THE CHLOROPHYLL APPARATUS 153 
appears to be the first carbohydrate to be formed ; itis 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,H,,0,, 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,,H,,0,,. This conclusion is based on repeated observations 
that when leaves of Tropeolum 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 
