40 VEGETABLE PHYSIOLOGY 
represented by the formula n(C,H,,0,), the value of » 
not having yet been accurately determined. This sub- 
stance is related to such bodies as starch, sugar, &c., 
being a member of the group of carbohydrates. It is 
capable, under the action of hydrating reagents, of being 
converted into a form of sugar, and under certain circum- 
stances it can yield nutritive material for the use of the 
plant. Cellulose possesses the peculiar property of becom- 
ing a deep blue in colour when treated with iodine in the 
presence of sulphuric acid, chloride of zine, or other hydrat- 
ing reagent. It dissolves with readiness in a solution of 
ammonio-cupric sulphate (Schweizer’s reagent), but is not 
soluble in dilute acids or alkalies. Strong mineral acids, 
such as sulphuric or phosphoric, cause it to imbibe water 
and swell up, ultimately becoming gelatinous and dissolv- 
ing. Certain soluble ferments affect it similarly. 
When the cell-wall is examined by polarised light it is 
found to be doubly refractive. 
When cellulose is oxidised with strong nitric acid it 
yields oxalic acid. 
Cellulose is capable of existing in more than one con- 
dition. We find some kinds of it which will stain blue with 
iodine without previous hydration. Examples of this 
variety are found in the cell-walls of the bast of Lycopo- 
dium, the endosperm of the Peony, the cotyledons of some 
of the Leguminose, &c. The walls of the hyphe of the 
fungi differ again, in that they will not give the blue colour 
with iodine even after treatment with hydrating reagents. 
Recent observations suggest that this variety of cell-wall ap- 
proaches in composition the chitin of the animal kingdom. 
The celluloses which have been so far examined have 
been divided into three categories, according to the ease with 
which they can be made to undergo hydrolysis, and to yield 
some variety of sugar by such treatment. The celluloses of 
cotton fibres are perhaps the most resistent of all, and may 
be taken as representatives of the most refractory group. 
The cellulose found in the main mass of the fundamental 
