CHLOROPHYCE 4 121 
as most probably nearer the lower limits of 
archegoniate plants than are any other Algz. 
The other Chlorophycee exhibit isogamous repro- 
duction—viz., the conjugation of equal gametes 
provided with cilia; and in the case of the Con- 
jugatee, which are confined to fresh-water, the con- 
jugation of non-motile gametes. 
Non-sexual reproduction by zoospores and un- 
ciliated spores also occurs freely and abundantly in 
the Chlorophycew. 
The Cawlerpacee, Vaucheriacew, Codiacce, Udo- 
teacee, Dasycladacee, and Valoniacew which form a 
group together (usually called Siphonew) are dis- 
tinguished from all other Algz by the fact that 
their often complicated thallus consists in reality of 
a single cell with many nuclei. In Valonia this one 
cell retains a primitive, more or less globular, shape, 
but in the other orders it is much branched and the 
branches gain coherence from being interwoven, laced 
together by haptera, incrustation, ete. In Caulerpa 
alone the lumen of the great cell is strengthened 
internally by numerous trabecule or crossbeams 
that run from wall to wall. 
CAULERPACEA. 
General Characters.—The order is represented by 
the single genus Cawlerpa (though systematists have 
proposed to split it up into several genera on wholly 
insufficient grounds) containing about eighty much 
varied species. They are exclusively marine. In some 
