Classification of some colonial Chlamydomonads. 1 5 i 
THE CLASSIFICATION OF SOME COLONIAL 
CHLAMYDOMONADS. 1 
By W. Bernard Crow, B.Sc., F.L.S. 
[With Two Figures in the Text] 
HE Isokontae show at least three distinct types of plant 
JL structure, the filamentous, the ccenocytic and the unicel¬ 
lular. The unicellular forms may be regarded as belonging to one 
order [21] although a few are best excluded in view of their 
probable origin by reduction from filamentous forms. This 
unicellular group is spoken of as the Protococcoideie [1, 19] or 
Protococcales [21], names which should be abandoned however 
because the generic name Protococcus has been used to denote a 
heterogeneous collection of Algae, and is now used [21, p. 191] to 
designate forms ( =Pleurococcus ) which are probably reduced 
members of the Ulotrichales. The name Volvocales is also 
unsuitable, since Volvox is not a typical representative of the 
group, and the term is in general use to indicate the motile 
members [14, 15, etc.]. On the whole the general characters are 
better expressed by the designation Chlamydomonadales, for the 
whole morphology of the group can be described in reference to 
that of Chlainydomonas. We are here only concerned with the 
normally motile members, which were formerly subdivided into (a) 
solitary (b) colonial forms [1, 2, 3, 6, 19], groups which are now 
known to represent different types of organisation rather than 
distinct lines of evolution. Some attempt has been made to 
arrange the genera in more natural families [14, 15]. Amongst 
the latter most authorities now admit the Sphaerellacefe to be 
distinct from the Chlamydomonadaceae, although a closely related 
line of ascent [4, 15, 17, 21, 22]. The following are the general 
tendencies of structure 
CHLAMYDOMONADACEA2. 
SPHAiRELLACEAJ. 
Envelope a thick coat, consisting Envelope a coat of variable 
of a thin outer membranous thickness, membranous to 
layer and a thick inner gela- gelatinous, usually not dif¬ 
ferentiated. 
tinous layer. 
Protoplasmic outgrowths travel’s- Protoplasmic outgrowths absent, 
ing pits in the membrane. 
> From the Botanical Department, East London College, University of 
London. 
