Classification of Green Algce. 
21 
(i antherozoid ) and fuses with the egg ( oosphere ), which is a purely passive 
and non-inotile megagamete, to form an oospore (oogamy). The germi¬ 
nation of the zygote or oospore may be direct or indirect. 
Reproduction may also be effected by detachment in the multi¬ 
cellular and ccenocytic forms of unspecialised vegetative parts from the 
thallus (fragmentation), by detachment and germination of slightly 
specialised immotile thick-walled cells (akinetes) which in the uni¬ 
cellular forms are produced by the direct metamorphosis of the 
vegetative individual, and by the formation of special immotile repro¬ 
ductive cells (aplanospores) due to the rounding off and investment with 
a new wall of one or more masses of protoplasm within a vegetative 
cell or coenocyte. 
[Many Algae belonging to various families of the Chlorophyceae 
have the power of passing into the “ palmelloid condition ” at the onset of 
unfavourable circumstances or of other changes in their environment. 
This condition is attained by abundant vegetative division, the daughter- 
cells, which are always rounded and devoid of specific characters, 
remaining aggregated within the confluent mucilaginous mother-walls. 
The phylogenetic significance of this biologically important phase is not 
clear.] 
Series I. Protococcoideae. 
Plant-body motile or immotile, most frequently unicellular or 
a simple globular coenocyte, often an indefinite mucilaginous colony oj 
loosely aggregated cells , sometimes a definite coenobium of cells or of 
simple coenocytes, never a definite multicellular thallus or a complex 
coenocyte. The whole range of reproductive processes characteristic 
of the Chlorophyceae is exemplified within this group. 
[This series is probably to be regarded as a grade-grouping of all 
the primitive forms of the Chlorophyceae, which may be considered to 
have been evolved from the Chlamydomonas-type, along lines exhibiting 
the divergent tendencies which find their higher expression in the other 
three series respectively.] 
(«) PLANT-BODY FLAGELLATE AND MOTILE DURING THE DOMINANT PHASE. 
Fam. I. Volvocaceae. 
Plant-body unicellular or consisting of a definite coenobium of cells 
which are either superficially coherent within a swollen mother-cell-wall 
or are united together by protoplasmic processes. All the cells, 
whether single or in coenobia, are flagellate and motile in the vegetative 
condition. 
Cells, rounded or more rarely tapering, with a specialised anterior 
end of non-granular protoplasm which bears 2 (rarely 4 ) flagella and 
contains usually two contractile vacuoles. A single nucleus in the 
centre, sometimes enveloped by the more or less basin-shaped chloroplast 
(colourless in Polytoma) which occupies the posterior end. Starch is the 
characteristic anabolite and one or more pyrenoids are found in the chloroplast. 
An eye-spot generally occurs on the periphery of the cell near the 
anterior end and a cell-wall is nearly always present. 
