crystals, called _raphides_.
The term is derived from [Greek: rhaphis] a _needle_, on account of the
resemblance of the crystal to a needle. They are composed of the
phosphate and oxalate of lime; but there is great difference of opinion
as to their use in the economy of the plant, and one of the French
philosophers endeavoured to prove that crystals are the possible
transition of the inorganic to organic matter. The differences, however,
between the highest form of crystal and the lowest form of organic life
known, viz., a simple reproductive cell, are so manifold and striking,
that the attempt to make crystals the bridge over which inorganic matter
passes into organic, is almost totally regarded as futile. In a layer of
an onion, a fig, a section of garden rhubarb, in some species of aloe,
in the bark of many trees, and in portions of the cuticle of the
medicinal squill, bundles of these needle-shaped crystals are to be
found. Some of them are as large as 1-40th of an inch, others are as
small as the 1-1000th. They are found in all parts of the plant,--in the
stem, bark, leaves, stipules, petals, fruit, roots, and even in the
pollen, with some few exceptions, and they are always situated in the
interior of cells. Some plants, as many of the _cactus_ tribe, are made
up almost entirely of these needle-crystals; in some instances, every
cell of the cuticle contains a stellate mass of crystals; in others, the
whole interior is full of them, rendering the plant so exceedingly
brittle, that the least touch will occasion a fracture; so much so, that
some specimens of _Cactus senilis_, said to be a thousand years old,
which were sent a few years since to Kew, from South America, were
obliged to be packed in cotton, with all the care of the most delicate
jewellery, to preserve them during transport.

[Illustration: SILICEOUS CUTICLE FROM UNDER-SIDE OF LEAF OF DEUTZIA
SCABRA.]

[Illustration: SILICEOUS CUTICLE OF GRASS.]

1076. Besides the cellular tissue, there is what is called a vascular
system, which consists of another set of small vessels. If, for example,
we, early in the spring, cut a branch transversely, we will perceive the
sap oozing out from numerous points over the whole of the divided
surface, except on that part occupied by the pith and the bark; and if a
twig, on which the leaves are already unfolded, be cut from the tree,
and placed with its cut end in a watery solution of Brazil-wood, the
colouring matter