CHLOROPHYCE 177 
PROTOCOCCACE 
General Characters—This is a very large order, 
very sparingly represented in the sea. Except in 
European seas, however, the marine forms have been 
little studied, and it is probable that many more 
types will be added in time, especially after a more 
extended examination of the floating Alge of the 
open ocean. The thallus is unicellular, and the cells 
are never associated intimately to form a tissue or 
definite group obeying a common law of growth. 
There are no cell-divisions during vegetative life. 
The plants are either stipitate or free, and never 
motile, unless of course in the zoospore stage. The 
conjugation of equal gametes has been observed, and 
also non-sexual reproduction by zoospores. 
The Thallus—Chlorochytrium and Chlorocystis in- 
habit the tissues of other plants, the former mainly 
flowering plants in fresh-water or on land, but also 
seaweeds, and the latter exclusively seaweeds. The 
cells are globular, oval, or irregular in shape, and 
the main vegetative difference between the genera 
appears to be in the shape of the chromatophores, 
and the fact that Chlorochytriwm has many pyrenoids 
while Cilorocystis has but one in each chromatophore. 
Chiorocystis Cohnit inhabits the tissues of many sea- 
weeds, and C. Sarcophyct causes deformities of the 
thallus of Sarcophycus. Halosphava is a beautiful 
globular form, living free in the ocean, and forming 
a considerable constituent of the plankton or floating 
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