FRESH-WATER ALG. 203 
which they naturally break through the tough and 
cartilaginous skin of the frond, in order to form 
independent individuals, is not the least curious 
circumstance in the economy of this strange plant. 
Bory, to whom we are indebted for the name, in- 
forms us that the recent filaments of the Lemania, 
when applied to the flame of a candle, explode and 
extinguish it, while a remarkable movement of re- 
traction is felt by the fingers which hold them. The 
plant is rich in nitrogen, and when burnt yields 
ammoniacal vapours. The spores at first vege- 
tate into slender filaments, which constitute a sort 
of prothallus or pro-embryo. From the cells of 
these filaments spring up after a time thick branch- 
lets, which are at first wholly dependent upon the 
cells from which they arise ; but they soon acquire 
rootlets at their base, and rapidly elongating grow 
into the cartilaginous bristle-like tufts character- 
istic of the mature plant. 
The conferve generally grow in single branch- 
less filaments, forming a loose fleecy stratum ; but 
sometimes they are aggregated together into sin- 
gular forms. There is one species known as the 
water-net or water-flannel (Hydrodictyon utricula- 
tum), which looks more like a piece of green baize 
manufactured by man, than a production of nature. 
It forms a beautiful tubular purse or net, with re- 
gular polygonal meshes articulated at the inter- 
