FRESH-WATER ALG. 249 
attached to the soil by a tuft of root-like fibres, 
into which their fluid contents descend when 
pressed. This singular provision is necessary, as 
the plant is frequently exposed to dry air, which 
absorbs the moisture on the surface of its native 
soil, and would consequently wither it, were it not 
furnished with radicles, which penetrate beyond 
the risk of desiccation. In the possession of this 
extensively ramifying root which enters the soil 
and absorbs nourishment, the Botrydium differs 
from alge in general, which have no genuine 
root, as they absorb nourishment through the 
whole of their tissues from the surrounding 
medium. It is truly a terrestrial plant, and is 
incapable of being developed under water, for 
submersion even for a few hours has the effect of 
bursting its globular head, and thus the spherules 
which it contains are set free and floated away 
from the parent to form new colonies. It also 
develops new individuals from its roots by a 
process of budding or vegetative increase. The 
Botrydium is a perfect miniature plant, with root, 
stem, bud, and fruit, in imitation of the most 
highly developed flowering plants, but strange to 
say, it is unicellular, consisting of one continuous’ 
cavity running through the entire plant. There 
are some very curious and little-known green 
alge allied to this plant, which are furnished with 
