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POPULAR SCIENCE REVIEW. 
swarm-spore. This mode of propagation by “ free-cell-forma- 
tion,” as it is termed, is one which has thrown great light on 
the constitution of the vegetable cell, clearly demonstrating 
that the vital principle of the cell resides not in its cell-wall of 
cellulose, hut in its protoplasmic contents, even when, as in the 
present case, the protoplasm does not possess a nucleus. The 
escaped zoospore of Vaucheria is, for all physiological purposes, 
a cell not enclosed in an envelope of cellulose, or a naked cell. 
As soon as the vibratile motion of the cilia ceases, the zoospore 
comes to rest, rapidly becomes encysted with a cellulose- wall, 
and grows into a new Vaucheria-plant by the ordinary process 
of cell-division. The separation of the protoplasm in the 
filament generally begins in the night, the zoospores escape in 
the morning, and their germination commences the next night. 
The sexual reproduction is accomplished by means of two dis- 
tinct organs (fig. 2 c, d , and e), the oogonia, or female cells, and the 
antheridia, or male cells, the two kinds being often produced in 
close proximity. From the protoplasm of the antheridium are 
produced a number of antherozoids, very minute long bodies, 
each with two cilia. At the time that these are ready to 
escape, the contents of the oogonium have swelled up into a 
jelly and burst the cell- wall; some of the antherozoids enter 
through the opening, mingle with the protoplasm in the interior, 
fertilising it, and causing it to assume the form of an oospore 
or 66 resting-spore,” which then developes into the new plant. 
The formation of the oogonia and antheridia begins in the 
evening, and is completed the next morning ; fertilisation being 
accomplished between ten and four in the day. Closely allied 
to Vaucheria is the very simple Botrydium ; but in other 
genera of Siphonese, the frond, though always consisting still of 
a single cell, assumes the most remarkable and beautiful forms, 
from the extraordinary extent to which it branches, as in 
Acetabularia Mediterranea (fig. 3), closely resembling in form 
a hymenomycetous fungus, and Gaulerpa taxifolia (fig. 4), 
where the frond actually simulates differentiation into stem, 
leaves, and roots. 
The (Edogoniece are a small family, including only two gene- 
ras, CEdogonium and Bulbochcete , but interesting as furnishing 
an illustration of a phenomenon more common among fungi 
than aigso — that of alternation of generations. From the 
oospores or resting-spores produced by a sexual process, which 
have remained at rest for a considerable time, several (usually 
four) swarm-spores are immediately formed; these produce 
asexual, i.e. swarm-spore-forming plants, from which again 
similar ones proceed, until the series is closed by a sexual 
generation, with formation of oospores. Swarm-spores are also 
produced in an ordinary cell of a filament by the contraction 
