ON THE JUICE OP THE SUGAR-CANE. 421 
made on that portion Btill covered with green leaves, sheltered from 
the direct action of the solar rays, there will be found in the ex- 
tracted juice a considerable quantity of uncrystallizable sugar which, for 
ripe canes, may be averaged at one-sixth of the weight of the crystal- 
lizable sugar ; and for unripe canes, at one-third of the same weight. 
It is then that the optical analysis leads to results considerably opposed 
to those of the chemical analysis ; and what is noteworthy, and also 
showing the necessity of further investigation, these results are not 
always identical, for the same quantity of sugar shown by the chemical 
process. Under certain circumstances dependent on the age of the cane 
and the vigour of its growth, perturbations result which can only be 
explained by the marked differences in the rotatory power of the un- 
crystallizable sugar existing in the juice extracted from this portion of 
the cane. The saccharine liquid always causes the plane of polarisation 
to turn to the right ; but after inversion, the notation to the left rarely 
agrees with the entire quantity of introverted sugar in the liquid, and 
is generally found to be represented by a figure lower than what should 
be attained. One instance from many I could cite, will be sufficient to 
give an idea of the considerable fall in value which such figure may un- 
go :— 
• Some juice extracted from the tops of some young Bellouguet canes 
with a density of 10*30 at a temperature of 25° centigrade, gave a direct 
notation + 8*3 ; and at 27° centigrade, an indirect notation — 6*1, which 
indicated after acidulation a total quantity of sugar equal to the seven- 
teen-thousandth part of the weight of the juice, whilst this very liquid 
really contained the fifty-four-thousandth part. 
The proportion of uncrystallizable sugar in the head as well as in 
the body of the cane, increases in proportion to the distance from the 
lowest part, the maximum quantity being found in that portion which 
is completely shaded from the light by the sheath of green leaves. This 
portion of the cane top, the bark of which is uncoloured and very tender, 
is, so long as it is protected from the action of the sun, the principal 
seat of the liquid sugar which the cane contains ; but immediately it 
becomes exposed by the drying of its leaves, it at once assumes ex- 
ternally a deeper tint, and at the same time the uncrystallizable sugar 
gradually disappears from its tissues, and yields its place to the real, or 
crystallizable sugar. This remarkable change can easily be observed on 
canes of the same kind and which form the same stems, by analysing at 
short intervals the portions of such canes more or less hid by the leaves, 
and then the corresponding portions of other canes as they drop their 
leaves and become tinted by the action of the light. 
3. The age of the cane has appeared to me to be only an indirect 
cause of the phenomenon here noticed. In placing young canes in the 
conditions of aeration, light, and growth usual to this plant when it 
reaches the term of its maturity, I have thereby stated nothing special 
