FRESH-WATER ALG. 231 
where frightful portents, apparently foreboding the 
most calamitous events, were no doubt owing to 
the excessive development, under peculiarly fav- 
ourable circumstances, of an exceedingly minute 
alga, bearing a strong superficial resemblance to 
the red snow plant. This alga was called by 
Ehrenberg the purple monad, under the impres- 
sion that it was an animalcule. More accurate re- 
searches, however, have since determined its vege- 
table nature, and it is now called Palmella prodi- 
gtosa, from the wonderful rapidity with which it 
develops and extends itself. The body of this’ 
cutious atom is but from the one three-thousandth, 
to the one eight-thousandth of a line (twelfth of 
an inch) in length. Like the red snow plant, it 
first of all appears in the form of small, bright, 
red points, like so many coloured minute dew- 
drops, or the roe of fishes, composed of inconceiv- 
able myriads of individuals, which afterwards unite 
into large red-currant-jelly-like patches, coalescing 
and penetrating the substances upon which they 
are produced. Its peculiar habit would seem 
rather to indicate affinity with the fungi than with 
the alge. Indeed by some authors it is now con- 
sidered a fungus, and classed among these plants. 
The accounts of blood-prodigies found in an- 
cient history, are matched by well-authenticated 
phenomena which have presented themselves 
