coloured infusion betrays the presence of vibratile ciliæ;
and we cannot believe that the threads turn on themselves,
because the granulations of the green matter do not change
place during the progression. I have seen threads of
three seeds move, hut never a single seed. I f you continue
to observe for some days, you will see the thread become
immoveable, increase in size, at the same time develope the
mucilage with which they are surrounded as with a transparent
sheath. Soon the seed enlarges considerably, and divides to
form two others, but sideways, and not in the direction of
the length of the threads.
“ This formation is repeated many times, and it would seem
natural to seek in this circumstance the origin of new
threads. Unfortunately the increase of the number of grains,
hy diminishing the transparency, prevents one following the
increase with the same facility. Their confused mass fills
entirely the young Nostoc, which is developed in a very irregular
manner, and takes a variety of forms. I t is but later
when the mucilage is most abundant, when the seeds are less
crowded in the interior of the Nostoc, th a t you begin to
distinguish the threads.”
The Nostochineoe of the first section are mostly of a lively
and exquisitely delicate green colour. They are wonderfully
prolific, increasing to such an extent frequently as to
impart their beautiful colour to extensive tracts of water,
as also do occasionally certain species of Oscillatorioe. One
species described by Mr. Thompson, Anahaina ? spiralis, and
Avhich I have named in honour of its discoverer. Spirillum
Thompsoni, imparted its colour to the entire of an extensive
lake, Ballydrain, which extends over about twenty acres of
ground near Belfast* The Oscillatoria ærugescens of Drummond
in like manner imparted its rich green colour to an
extensive lough in the north of Ireland, Glaslough, whose
waters seemed greened as though by the reflection of trees, f
* For an interesting paper, by Mr. Thompson, on this Alga, see
“ Annals of Nat. Hist.” vol. v.
t See Annals Nat. Hist. vol. i.
Leaving the limits of our own country, MM, Engelhardt and
Treschel have described a minute Alga, which they have named
Oscillatoria rubescens, and which tinges with a red colour
the lake of Morat, in Switzerland, assuming sometimes a
very beautiful arrangement, depending upon the motion of
the water in which it is immersed.*
B u t it is not in fresh water merely that the productions of
this family are found; they likewise have been noticed to
occur in vast quantities in the sea, in different parts of the
world; and it has been ascertained that the Red Sea owes its
name to the periodical developement of a species of this
family, the Trichodesmium Ehrenbergii Montagne. The
name of Ehrenherg has very properly been appended to
this species by Dr. Montagne, that illustrious naturalist
being not merely the first to describe the species, but also
the first to discover and record the important and wonderful
fact that to a production in its individual parts so minute and
insignificant, the Red Sea owes its name and appearance.
This interesting discovery, however, of Ehrenherg was for
many years overlooked, the account of it having been published
in a work not devoted to natural history, but to
chemical science, “ Annals of Poggendorf.” The following
translation cannot fail to in te re s t: —
“ During the year 1823,” observes M. Ehrenherg, “ I made
a stay of many months at Tor, upon the borders of the Red
Sea, close to Mount Sinai. On the 10th of December I there
saw the surprising phenomenon of the blood-red colouration
of all the bay which forms the port of that city. The high
sea, without the boundary of the corals, preserves its ordinary
colour. The short waves of a tranquil sea bring upon
the banks during the heat of the day a mucilaginous matter
of a blood-red colour, and deposit it upon the sand, in such a
manner as that in the course of a good half hour all the hay
with the receding tide is surrounded with a red border of many ■
* Notice sur la matière qui a coloré en rouge le lac Morat, en 1825, par
De Candolle, dans les Mémoires de la Société de Physique et d’Histoire
Naturelle de Science, 1825, vol. ii. with fig.