^9 
Classification of Green Algce. 
A REVISION OF THE CLASSIFICATION OF 
THE GREEN ALG^ 
BY 
F. F. Blackman, 
University Lec-iurer in Botany , Cambridge. 
AND 
A. G. Tansley, 
Assistant Professor of Botany , University College , London, 
(continued from page 72.) 
**Selenastracea. 
Body either unicellular or an indefinite colony or a true 
ccenobium. Cell of very various shape, rarely spherical 
or oval, often pointed at one or both ends, very frequently 
reniform or semilunar, sometimes flattened. Cell-wall 
typically of an inner, thin, closely-adherent membrane, and 
an outer, mucilaginous coat, which is sometimes produced 
into processes, and by which the single cells often adhere 
together. Chromatophore single, parietal, often basin-shaped, 
but frequently occupying nearly the whole of the cell, usually 
with a single pyrenoid. 
Reproduction by vegetative division, typically into four cells 
enclosed within the mother cell-wall. The four daughter 
cells may either separate at once by diffluence of the mother 
wall, or remain together, typically adhering by their mucila¬ 
ginous coats, often to form definite coenobia. Zoospores and 
gametes entirely unknown. 
[This group includes the majority of the typical Pleurococcaceas of 
Klebs, and seems a very natural one. The general features of the 
cell-type are remarkably constant and the group can be theoretically 
derived from a Chlamydomonadine ancestor in which the formation of 
flagella has been suppressed, and the cell has become elongated and 
often curved. In the simplest genera the cells live singly but shew a 
tendency to remain connected after division. From this type more or 
less definite colonies seem to have been evolved in various directions. 
The prevalence of the crescentic form of cell is a marked feature of the 
group. 
The name we have adopted is taken from a fairly typical genus 
and has the advantage of calling attention to the prevalent crescentic 
cell-type, as well as to the radiating structure often exhibited by the 
colonies.] 
Series A. Cells rounded or pointed and sometimes curved; floating 
freely , either singly, or slightly adherent to form indefinite colonies. 
7 . Dactylococcus .’ Nageli, 1849 . 
Cells oval or pyriform, often apiculate, single or loosely 
coherent by their pointed ends. 
’This genus has generally been placed among the Tetrasporaceae, 
and we followed tradition in including it among the genera of 
doubtful affinity belonging to that artificially defined family, 
but the most careful existing account denies the existence of 
zoospores, and assigns it characters which clearly give it a 
natural position among the lower members of our Selenas- 
trace*. We have therefore introduced it again in this place. 
