32 
POPULAR SCIENCE REVIEW. 
which the frond forms a beautiful net, Coleochcete , which 
consists of cushions of jointed threads, attached to submerged 
plants, as Equisetum, and many others. 
Sometimes included under the Confervaceae, but often sepa- 
rated in consequence of the peculiarity of its physiological 
phenomena, is a small family, the Saprolegniece , including the 
two genera Saprolegnia and Achlya. If the dead body of a 
fly floats for a little while on water, it rapidly becomes covered 
on the under side by a coating of fine white hairs, constituting 
the alga known as Acltlya prolifer a. If, on the other hand, 
the dead fly is exposed to dry air, as on a window-pane, it 
also soon becomes surrounded by a number of white threads, 
the mycelium of the well-known fungus Empusa Muscce. 
Many cryptogamists are of opinion that these two organisms, 
the one an alga, the other a fungus, are simply different states 
of the same plant, produced under different circumstances ; 
while others consider the Achlya to be an aquatic form of a 
Botrytis , or of some other fungus. In any case, this remarkable 
fact proves the extremely close affinity between the lower forms 
of these two great classes of flower less plants. 
2. The Fucoide^i includes an enormous number of marine 
algae, of brown or olive colour, mucilaginous in texture, and of 
very variable form. To this order belong the largest and 
noblest of seaweeds, of shrubby or even arborescent form, 
rivalling the tallest trees in the actual length of their 
branches ; as the Lessonia fuscescens and the gigantic Macro - 
cystis pyrifera, represented in our Plate (figs. 11 and 12), 
from the Antarctic Seas, and the historic Sargassum bacci- 
ferum , or Atlantic Gulf-weed. The detached masses of this 
sea-weed form a floating meadow, known as the “ Sargasso-sea,” 
in the midst of the Atlantic, between 20° and 25° H. lat., and 
about 40° W. long., and occupying an area estimated to equal 
in size the whole of France. This enormous field has certainly 
occupied the same position since the time of Columbus, whose 
first expedition was so seriously delayed by it that the sailors 
were on the point of mutiny when a favourable wind carried 
them beyond it. It consists entirely of floating masses, buoyed 
up by the stalked berrv-1 ike air-bladders, from which it derives 
its name, but never producing fruit. It forms the home of 
multitudes of sea-animals, fishes — one of which builds a nest — 
and Crustacea, many of which, we learn from the reports sent 
home by the 66 Challenger ” expedition, furnish remarkable 
instances of “ protective mimicry,” closely resembling in colour 
the sea-weed in the midst of which they live, this being their 
only protection against their enemies. 
Thuret divided the Fucoideae, or Melanosporeae, into two 
groups, of which the Phaeosporeae, including Laminaria , 
