i 14 Blackman and Tansley. 
A REVISION OF THE CLASSIFICATION OF 
THE GREEN ALG^E 
BY 
F. F. Blackman, 
University Lecturer in Botany , Cambridge. 
AND 
A. G. Tansley, 
Assistant Professor of Botany , University College , London, 
{continued from page 96 .) 
Fam. VI. Hydrodictyaceae. 
Plant-body an immotile ccenobium of ccenocytes, formed by the 
apposition and anion of free zoospores which, however, have not 
escaped from the mother ccenocyte. Reproduction also by isogametes. 
Germination indirect, the zygote increasing in size and producing 
swarmers which come to rest and form “polyhedra” in which zoospores 
are produced, and by apposition and union give rise to new ccenobia. 
1 . Euastropsis. Lagerheim, 1894 . 
Ccenobium of two ccenocytes (?). Zoospores 2 - 32 , 
joining in pairs to form one or more ccenobia in each 
mother-ccenocyte. Gametes unknown. 
2 . Pediastruin. Meyen, 1829 . 
Ccenobium of 2 - 64 ccenocytes, forming a plate, continuous 
or with gaps. Marginal ccenocytes generally lobed, and 
with the wall extended into horns. Chromatophore 
parietal with one pyrenoid. 
3 . Hydrodictyon. Roth, 1800 . 
Ccenobium of very numerous large cylindrical ccenocytes, 
each of which may attain 1 cm. in length, joined end 
to end to form a net extended in three dimensions. 
Protoplasm in each ccenocyte lining the wall and 
enclosing a large central vacuole. No separate 
chromatophore; the whole of the cytoplasm, except 
the ectoplasm and vacuole wall, containing chloro¬ 
phyll, and with pyrenoids and nuclei distributed 
through it. 
Series 2 . Siphonales. 
Thallus a ccenocyte or an aggregate of ccenocytes , usually taking 
the form of a branched filamentous system, fixed below to a 
substratum, the branches free or secondarily attached to one another 
or interwoven to form a more or less massive thallus. Protoplasm in 
a parietal layer, surrounding a central vacuole and containing 
numerous nuclei; chromatopliores usually numerous, oval or angular 
discs, with or without pyrenoids. 
Reproduction by means of biflagellate (rarely quadriflagellate) 
