650 Blackman. — The Primitive Algae 
one based on the coenocytic structure of the thallus, and will 
probably remain long unchanged. The other groups are not 
natural, and must before long be abandoned. 
The Confervoideae contain those types of organization 
which are filamentous or membraneous, and which are uni¬ 
versally accepted as forming one step in phylogenetic ascent 
from the lowest unicellular Algae to the higher plants. 
The Protococcoideae seem to have been first segregated as 
a heterogeneous remainder of primitive forms left after the 
characterization of the other two groups. In the Protococ¬ 
coideae we find all grades of sexual reproduction up to oogamy 
( Volvox ), and many different types of vegetative organization : 
motile single cells ( Chlamydomonas ), non-motile single cells 
(Endosphaereae), loose indefinite colonies ( Tetraspora ), defi¬ 
nite coenobia of motile ( Volvox ), or of non-motile cells 
(Coelastrum ), and even coenobia of coenocytes (. Hydrodictyon ). 
Some of these organisms live entirely by vegetative division, 
and others are characterized by never dividing vegetatively. 
This chaos of forms resolves itself, when studied inductively, 
into some ten more or less natural groups (sub-families of 
Wille); cf. p. 6 49. 
Among this group of families there are three divergent 
vegetative tendencies, which furnish, I think, the natural broad 
phylogenetic lines on which to arrange the different types. 
These I would distinguish as follows:— 
The first of these tendencies, the Volvocine, is towards 
the aggregation of motile vegetative cells into gradually 
larger and more specialized motile true coenobia. 
The second, or Tetrasporine, is towards the formation of 
aggregations by the juxtaposition of the products of septate 
vegetative cell-division to form non-motile organisms of 
increasing definiteness and solidarity. 
The third, or Endosphaerine, tends towards the reduction 
of vegetative division and septate cell-formation to a minimum. 
The organisms on this line are strictly unicellular and non¬ 
dividing when primitive; unseptate coenocytes when more 
advanced in type. 
