have been carefully exaiuiiied. During a tour in Languedoc
and the Auvergne, in the spring of 1854, I made upwards
of forty gatherings from tlie rivers, streams and lakes of the
district I traversed; in these I detected one hundred and thirty
species, described in the present work, and but one form not
yet determined as indigenous to Britain. If this be the case
with a district, much of whose Phanerogamous flora is so different
from onr own, it bears out tlie view I have taken, that
these organisms enjoy a range of distribution far more general
than the higher orders of plant-life.
Nor is the distribution of marine species less notable for its
extent and uniformity. Coscinodismis eccentricus and Coscino-
discm radiatus range from the shores of Britain to those of
Southern Africa. Grammatophora marina and Grammatophora
macilenta are found in almost every marine gathering from the
Arctic Ocean to the Mauritius. Stauroneisptdchella, Cocconeis
Scutellum, sxiA BtddulphiapulclieUa are equally abundant on the
European, the American, and the African coasts; while Bhabdonema
Adriaticmn belies its name by its occurrence in the Indian,
Atlantic, and Pacific Oceans. During the researches already
mentioned in the South of France, I made several prolific
gatherings on the shores of the Gulf of Lyons; but of thirty-
three forms occurring in these, Hyalosira delicatula, Kiitz,, was
the only one not familiar to me as a British species.
Of the purposes served by the wide diffusion of these organisms
it is impossible to speak with certainty. Their minute
size forbids us to attribute much effect to their individual influences
; but when we regard them as aggregated in numbers that
defy enumeration, we are compelled to believe that they occupy
an important place and subserve necessary ends. Their nutritive
process, which involves the absorption of carbonic acid and the
extrication of oxygen, must tend to preserve the purity of the
water in which they are found, and to prepare it for the respiration
of aquatic animals. Their presence in the stomachs of Infusoria,
Annelida, Mollusca, and Crustacea, shows that they constitute
to some extent the food of these animals; and the vast
numbers of their siliceous valves which occur in Guano, prove
that they are swallowed in large quantities by birds, and minister
to their sustenance. Their direct uses to man are probably
few and unappreciable, except in the mechanical arts, where, as
I have before stated, the powdery debris of their frustules, from
its siliceous character, is profitably employed as a polishing
material ; indirectly they doubtless contribute to the fertility of
the soil, and promote the growth of many of the cereal grains
which furnish the human family with the farinaceous elements
of food. This is the more probable, if it be true, as Ehrenberg
and other writers have asserted, that moist ground everywhere
exhibits the presence of these organisms. A singular instance
in illustration of this has been mentioned to me by Dr. Gregory,
who states, that upon examining the particles of earth adhering
to the roots of plants collected in various and widely separated
localities, he almost invariably detected Diatomaceæ.
The result of the presence of these forms in vegetable mould
must be the extrication of silica from the fluids in the soil, and
its deposition after the death of the Diatomaceæ, in another
condition, that may, in some unexplained manner, minister to
the healthy growth of larger plants.
But even should we fail in our attempt to explain the precise
objects of the Diatomaceæ in the economy of being, we may
rest assured that organisms of such infinite variety have not
been formed in vain ; and that the time we may occupy in the
study of their functions, or in the admiration of their marvellous
symmetry, will not have been idly spent, if it enhance our conceptions
of creative skill, and strengthen our persuasion of the
omnipotent power and diffusive energy of the divine Artificer
of Nature.