CHLOROPHYCE& 133 
of reproduction, viz. by zoospores. It is consequently 
an aberrant type, but its inclusion may be justified 
on grounds dealt with later. 
The Thallus—The beautiful feather-like fronds of 
Bryopsts recall the habit of certain species of Caulerpa, 
but between the genera there is little more than this 
superficial resemblance. Wille has stated that in 
old stalks of Bryopsis trabecule sometimes occur, but 
the observation is open to question. If established, 
it would certainly help in the elucidation of the 
position of Caulerpa, especially when taken together 
with the observation of Correns (p. 124) on the 
character of the cell-membrane. The thallus of 
Bryopsis consists of a single branching cell differ- 
entiated into rhizoids and erect shoots. The shoots 
consist each of a primary stalk, which either itself 
bears the ultimate lateral branches (which for con- 
venience may be called leaves with apologies to 
formal morphology) or it may first branch repeatedly. 
The variations in this respect and in the occurrence 
of the leaves, whether opposite, alternate, secund, or 
in irregular spirals round the stalk, are characters of 
use in the discrimination of the species, though they 
are to be used with caution, since variation occurs 
within certain limits. The erect feathery fronds of a 
beautiful deep green are not only very graceful, but 
furnish objects of much interest for the microscopical 
study of the cell. In the middle of the cell is a 
vacuole, and the protoplasm lining the wall contains 
numerous nuclei and oval, flat chromatophores, each 
with one pyrenoid. Bryopsis, like Derbesia, Vaucheria, 
and Caulerpa, has all its filaments free, and not 
