COLOSSAL ALGA, 89 
by the same colouring matter—the substance called leaf- 
green, or chlorophyll—which colours the leaves of all the 
higher plants. 
To this class belong, besides a great number of low 
marine Algze, most of the Alge of fresh water, the 
common water hair-weeds, or Conferve, the green slime- 
balls, or Gloeosphzerze, the bright green water-lettuce, or 
Ulva, which resembles a very thin and long lettuce leaf, 
_and also numerous small microscopic alge, dense masses of 
which form a light green shiny covering to all sorts of 
objects lying in water—wood, stones, etc. 
These forms, however, rise above the simple primary Algz 
in the composition and differentiation of their body. As 
the green Alge, like the primeval Algze, mostly possess a 
very soft body, they are but rarely capable of being petrified. 
However, it can scarcely be doubted that this class of Algze 
—which was the first to develop out of the preceding 
one—most extensively and variously peopled the fresh and 
salt waters of the earth in early times. 
In the third class, that of the Brown Tangles (Pheo- 
phyceze), or Black Algw (Fucoides), the branch of the Algeze 
attains its highest stage of development, at least in regard 
to size and body. The characteristic colour of the Fucoid 
is more or less dark brown, sometimes tending more to 
an olive green or yellowish green, sometimes more to a 
brownish red or black colour. 
Among these are the largest of all Algz, which are at 
the same time the longest of all plants, namely, the 
colossal giant Algze, amongst which the Macrocystis 
pyrifera, on the coast of California, attains a length of 
400 feet. Also, among our indigenous Ale, the largest 
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