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whicli dry up and disappear at the approach of summer, the
species inhabiting them having performed their allotted office
in the economy of nature, disappearing likewise, their lives
terminating with the exigency which called them into existence
; others are usually met with in the perennial waters
of our deep and clear lakes and ponds, and, though not themselves
perennial, yet have probably a life of somewhat
longer duration extended to them ; as, for example, some of
the larger Zygnemata, certain species of Draparnaldia
and Lynghya and Conf. crispata. I am inclined to think,
however, that the lives of but few species of freshwater
Algæ extend beyond the period of a year, while it is very
certain tha t very many perish in a few months, or even
weeks, from the time of birth, in which case I can assert
from observation, that the species perishing thus early are
frequently reproduced in the course of the summer, when
the circumstances are favourable, some two or three times.
Very many Conferva die in the spring from the drying up
of the waters in which they dwell, at which season it is
wisely ordained that such species should mature their seeds ;
amongst these may be mentioned many species of the genera
Zygnema, Tyndaridea and Vaucheria ; others die at the approach
of winter, but not all; a few linger through the
greater part of this season so unfavourable to the exercise of
the vital functions of plants. There are other species, again,
Avhlch do not require to be constantly immersed in water,
but are found upon those soils and in situations which retain
moisture for some time, as upon shaded and clayey pathways,
at the roots of trees, on banks, thatch, and at the bottom of
palings, the drippings from which they receive. In such localities,
Conf. ericetorum, some Lynghyea, Scytonemea, many
Oscillatoria and Nostochinea are met with. In these plants,
the strength of the vital principle must be very great, for
their filaments may be dried up for a considerable time ; but
on the application of moisture, they soon recover their
healthy appearance.
So abundant are the productions under our consideration,
that there is not a ditch or pool of any extent or standing
but furnishes one or more species, and even our mineral
springs are not entirely free from them. From the uniform
nature of the element which the majority of the freshwater
A lg a inhabit, it may be confidently anticipated that very
many of the species described in this work will, when the
A lg a come to be studied with that diligence and care which
they so well merit, be found in most of the continental
countries. Of the species described by Vaucher, a considerable
proportion are likewise indigenous to Great Britain.
Most of the freshwater Conferva, when in a healthy state,
are of a green colour, the shade being often extremely rich
and beautiful, but varying with the condition of the species,
and with the species themselves. The occurrence of this
colour is comparatively rare amongst the marine Alga, In
which it is usually more or less red or brown, the colouring
matter being operated upon probably by free acids in the salt
water.
Sometimes the Conferva are diffused through the waters
of a pond or lake, imparting to it a bright green colour, and
causing it to resemble so much of the purer element— the
sea. A t others, the filaments of a number of different species
will become entangled, and fioat together upon the surface of
the water, wafted hither and thither by the wind, like a
beautiful cloud, the softness and richness of the tints of which
a painter would he immortalized could he imitate. I t is only
during the early spring months, however, tha t the Conferva
retain this depth and beauty of colouring; for under the
influence of the rays of the summer sun, they very soon fade
and bleach, becoming ultimately, when the water in which
they dwell has evaporated, converted into the paper-like
substance which has recently attracted so much attention on
the Continent; indeed, so like to artificial paper is this
natural formation, that I feel assured an useful paper might,
by an artificial process, be made during the summer months
out of many abundant species of Conferva.
The Conferva, like most other productions, whether animal
or vegetable, whose organization is feeble, cling tenaciously
to life ; thus, they may be torn and cut up into a thousand
D 3