SEAWEEDS AND PONDWEEDS A7 
water nearly reaches the boiling point, in the depths of 
the sea and on the tops of the mountains, on hard 
gravel paths and in any wayside puddle. Sometimes they 
live quietly within other plants, as in the bog moss, and 
one particular species has taken for its home the feet of 
the three-toed Sloth! 
Just in the same fashion they vary in size. Thousands 
of species are quite microscopic, while others in tropical 
seas are of the thickness of a man’s thigh, or perhaps 
cover the surface in a vast mass, which may delay the 
progress of a ship. Such a case is shown in the Atlantic 
in the “Sea of Sargasso,” where for miles and miles the 
water seems but a tangled mass of weed. 
As yet the classification and arrangement of all these 
countless individuals are incomplete and uncertain, but a 
general idea of the progress of development up to the 
mosses can be obtained by grouping them according to 
the manner in which they produce fresh individuals. 
In the lowest group come all those which, so far as we 
know, only form fresh plants by splitting themselves into 
two or more. Most of these consist simply of a single 
cell, and as a rule they live in large colonies, forming 
green patches on submerged stones, or sometimes on 
trunks of trees. Their enormous number may make 
them important, for on one occasion (see Kerner and 
Oliver, II, 621) “a form, probably referable to this 
group, made its appearance off the Adriatic coasts in 
such numbers as seriously to interfere with the fishing 
industry. A commission was appointed to investigate 
the matter, but in six weeks it vanished as suddenly 
as it had appeared.” To tell the truth, as yet we do not 
know very much of the history of these plants. 
The second group includes those that effect repro- 
