674 Blackman .— The Primitive Algae 
The whole of the elongation of the growing cell has been 
produced by the apposition of layers inside the lower half 
with cotemporaneous extension and elongation of tnem so 
that the lower half of the cell behaves just like half a growth 
unit of the Conferva type (cf. the schema in Fig. 14 ; a is the 
young cell and b a half-grown cell). The two genera are 
thus closely related, but one is unicellular and the other 
pluricellular, so that we have here another case against 
primary groups based on these characters. 
The yellow-green chromatophores of this group give a blue 
odour with strong hydrochloric acid due to the abundance 
of xanthophyll, while typical Chlorophyceae become yellow 
when so treated. In bright light, fine refractive granules are 
first produced in the cell, and as assimilation goes on these 
run together to form large oil-globules, soluble in chloroform 
but not in alcohol. A small amount of hexose can be 
extracted from the cell by water, and it is probably the 
earliest product of assimilation and reduced afterwards to fat. 
Vaucheria seems to be the only green Alga outside the 
Confervales which has chlorophyll possessing these characters. 
What phylogenetic significance this may have is at present 
doubtful. 
The very close relation of Ophiocytium with Conferva leads 
Bohlin to rearrange the genera within the Confervales into 
three families. 
I. Confervaceae , thallus uni- or multicellular, gametes bi- 
ciliate, no pyrenoids. 
Conferva , Ophiocytium , Bumilleria , Botrydiopsis. 
II. Chlorotheciaceae , cells single or a thallus, gametes uni- 
ciliate, no pyrenoids. 
Misckococcus, Peroniella , Characiopsis , &c. 
III. Botrydiaceae , thallus unicellular showing root and shoot, 
multinucleate, pyrenoids present in young plant. Botrydium. 
Among the Flagellata there is a form which has some of 
the Confervales characteristics, namely a number of discoid, 
yellow-green chloroplasts without pyrenoids. This is the 
genus Vacuolaria (Cienkowski, ’ 67 ) (Fig. 14) of the Chloro- 
