Our Fresh- Water Alga. 675 
into discs, as Coleochzete, some expand into a leaf-like membrane, as 
Prasiola, or widen from hollow spheres and tubes into broad 
undulating sheets like the Tetrasporas, others grow in solid globular 
masses, as the Cheetophoras, one species of which occurs in the form 
of little green balls like peas, and hangs on dry grasses and other 
supports in quiet pools in spring. Others of looser texture, expand 
into an indefinite and irregular mass which will crumble at a touch, 
or form a gelatinous stratum which slips like oil through fingers 
that endeavor in vain to raise it from the water. Many others 
» become firmly adherent crests on rocks, especially under falling 
water. Most of the more beautiful species become filaments, 
usually formed of cells placed end to end, sometimes composed ot 
several or many such filaments bound together, either branching or 
not, and attaining particularly fine development in the Batracho- 
sperms, where the many branched and forking filaments are clad 
with radiating whorls of smaller branches, often in the most perfect 
regularity. 
Very commonly gelatinous in substance, many of the larger 
species are too frail to bear lifting out of the water, and yet endure 
considerable stress of their native current without harm, swaying 
with graceful motion as becomes beings born to the water. As 
there are all degrees of consistency in jellies, so there are in alge, 
from the tough jelly of a Prasiola, to the fluid jelly of a Tetraspora. 
Professor Wood named his genus Pagerogala, “ frozen milk,” from 
its seeming to float like white curds of clotted milk in a Pennsylva- 
nia spring. Some Draparnaldias may fairly be called succulent, 
others approach nearest of any of our alge to the wiry character ; 
the Lemanea issometimes almost leathery ; Spirogyras feel under the 
fingers like a lock of hair ; some of the largest Confervee are tough 
enough to support considerable weight, and have such strength of 
fibre that German ingenuity has tested their capability for textile 
use, and not only made mattress-stuffing and paper from them, but 
actually fabricated them into coarse trowsers, as if to show that the 
common phrase “clad in weeds” is not incapable of the most literal of 
fulfilments, Stranger still than any Confervæ, are the mailed knights 
among the alge, the little diatoms, absolutely unyielding and en- 
cased in silex, like so many little glass boxes under the microscope 
all curiously chased and set with flashing points and knobs. Some of 
