the magnification employed. That there are faults no one will
deny ; but, on the whole, we are not prepared to condemn it as
unworthy of the time at which it appeared. A comparison of
the Desmids with those in Ealfs’ work, of but three years
later, will show th a t in execution something was left to be
desired.
The third epoch is one on which we must necessarily be very
brief ; coming so near our own time we must be content to indicate
what has been done, and leave conclusions to others.
Closer relations with the Continent, cheap postage, more general
acquaintance with foreign works, all tend to raise greater expectations
for the closing work of the third epoch than of its predecessors.
The works of K utzing, the Memoirs of Pringsheim,
De Bary, Cohn, Bornet, Thuret, Borzi, Wittrock, and many
others, all contribute to illustrate British Fresh-Water Algæ;
and although during forty years very little has been done in our
own island, even in the identification of species, there has been
considerable activity in investigation, especially in the North of
Europe. The scattered memoranda, notes and observations of
Professor Henfrey, Dr. Braxton Hicks, and Mr. W. Archer
constitute the bulk of our home manufacture of the literature of
Fresh-Water Algæ for about 30 years. The later portions of
the “ Supplement to English Botany,” containing Algæ, date
from 1843 ; and Harvey’s second Edition of the “ Manual,” in
1849, was wholly confined to Marine species. Hence there is
not an independent work on British F resh-Water Algæ belonging
to this third epoch, the only contributory work being Berkeley’s
“ Introduction to Cryptogamie Botany,” in 1857. But if there
was an extraordinary dearth of books on this subject after 1845
in Britain, such was not the case on the Continent. The consecutive
publication of the volumes of Kutzing’s “ Tabulæ ”
must have been an important influence, although it was not
until 1864 th a t Rabenhorst’s “ Flora Europæa Algarum, Aquæ
Dulcis et Submarinæ ” was commenced. The advent of this
work was hailed with pleasure, notwithstanding its many faults;
and various authors set themselves to work on different genera
and families, such as Ædogoniaceæ, Zygnemaceæ, &c., so th a t
in twenty years it is left far behind. As a work written in E nglish,
although not containing much original observation, we
must mention Dr. Horatio Wood’s “ F re sh -W ate r Algæ of
North America,” published in 1872. The period selected,
therefore, for a new work on the “ British Fresh-Water Algæ ”
was in all respects opportune, but we are not expected to judge
whether good use has been made of the opportunity.
The gradual accession to knowledge of the structure and
development of Algæ, during the past century, would extend
this chapter far beyond the limits we have assigned to it,
whereas an intimation of the present position is generally indicated
under the several groups, in the body of the work, with
some reference to the sources of further information.
Classification must, of course, depend very largely upon
investigation, and modifications necessarily follow new facts, so
that, whilst adopting suggestions made by authors of recent
monographs, our arrangement is not absolutely th at of any
other work, although as far as possible the orders and larger
groups have not been disturbed. We will not venture to predict
what will be the future of such families as the Palmellaceoe,
Protococcacece, and Chroococcacece during the next twenty years ;
probably they will disappear altogether, becoming merged into
other groups of which most of them may be demonstrated to be
only imperfect conditions. A t the present time we could follow
no other course than to include them, and leave the future to
take care of itself. We have preferred including too much to
excluding too much, in confidence th a t for this we should be
the more readily forgiven.
The student will expect to find in this place some practical
hints to guide him in his pursuit, but these must be brief, as
experience, combined with a little personal contact with old
hands at field-work, will supersede a volume of precepts.
The habitats attached to the various species will indicate
the kind of locality in which to search for them, but it may be
remarked that, generally, any slow stream, pond, or standing
pool will furnish something. Rapid currents will not repay the
search. Small pools on moors, amongst Sphagnum, will usually
prove prolific, and submerged plants, especially when dead or
dying, often serve as a habitat for attached species. Damp
rocks, down which the water trickles, old quarries, damp walls