large quantities. It is met with in the roots of the dandelion,
chicory, and many other plants.

_Gum_ is an abundant constituent of plants. The kind termed gum
arabic, so largely employed in the arts, is a very pure variety of this
substance. Common gums are said to be essentially composed of a very
weak acid--_gummic_, or _arabic_ acid--united with lime and potash.
The solution of gum is very slightly acid, and has a mucilaginous,
ropy consistence: it is almost tasteless. _Mucilage_, or _bassorin_,
is simply a modified form of gum, which, though insoluble in water,
forms a gelatinous mixture with that fluid. It exudes from certain
trees--the cherry for example--and exists largely in linseed and other
seeds. Gums are nutritious foods, but it is probable that they are not
equal in alimental power to equal weights of starch or sugar.

_Vegetable jelly_, or _pectin_, is almost universally diffused
throughout the vegetable kingdom. It is owing to its presence that the
juices of many fruits and roots possess the property of gelatinizing.
It is soluble in water, but prolonged boiling destroys its viscous
property. _Pectose_ is a modification of pectin; it is insoluble in
water. According to Fremy, the hardness of green fruits is due to the
presence of pectose; which is also found in the cellular tissue of
turnips, carrots, and various other roots.

_Cellulose_ is a fibrous or cellular tissue, allied in composition to
starch. It is the most abundant constituent of plants, and forms the
very ground-work of the vegetable mechanism. Linen, cotton, and the
pith of the elder and other trees are nearly pure forms of cellulose.
Ligneous, or woody tissue (_lignin_) is indurated cellulose, hardened
by age. It is almost identical in composition with cellulose. Pure
cellulose is white, colorless, tasteless, insoluble in water, oil,
alcohol, or ether. It is heavier than water. Sulphuric acid is capable
of converting it into grape, or starch sugar. In its fresh and succulent
state cellulose is digestible and nutritious; but in the form of
ligneous tissue it opposes a very great resistance to the action of the
digestive fluids. Digestible cellulose is probably equal in nutritive
power to starch.

_Oils and fats_ occur abundantly in vegetables, more particularly in
their seeds. In the seeds of many cruciferous plants the proportion
of fat and oil exceeds 35 per cent. The oils and fats termed _fixed_
are those which possess the greatest