THALLOPHYTES 15 
(i) CHLOROPHYCEAE 
General character. The green algae usually contain no pigment in 
addition to the chlorophyll, and their appearance justifies the name. 
They include the simplest algae, and are generally supposed to be the 
forms from which the higher groups of plants have been derived. On 
this account green algae may be regarded as the beginning of our 
present vegetation. The protoplast always has a distinct nucleus and 
one or more chloroplasts, and this mode of organization is continued 
throughout all the higher green plants. As presented here, the Chloro- 
phyceae contain six distinct groups, as follows: Volvocales, Protococ- 
cales, Confervales, Siphonales, Conjugates, and Charales. It is recognized 
that some of these groups are very artificial, and that some of them per- 
haps should be set apart from the Chlorophyceae; but in this elemen- 
tary presentation of the forms, it is more convenient and less confusing 
to use this grouping. The doubtful situations will be indicated in 
connection with the different groups. 
(a) Volvocales 
General character. These aquatic forms are distinguished from 
other green algae by the fact that the vegetative cells have cilia and 
therefore are motile. They are sometimes regarded as animals, 
for they grade plainly into the Flagellates, a 
group of organisms of mixed plant and animal 
affinities (see p. 20). A few representative 
forms will indicate the structure and tendencies 
of the group. 
Chlamydomonas and Sphaerella. Chlamydo- 
monas consists of a single cell bearing two cilia, 
the protoplast being closely 
invested by a thin membrane 
(fig. 21). The structure of 
Sphaerella is in general the FIG. 21. CMamydo- 
same except that the cell **" showing the hup 
cuphke chloroplast, the 
FIG. 22.Sptuierella: has a lo Se membrane, embedded pyrenoid, the 
showing the protoplast which is connected with the centrally placed nucleus, 
invested by a loose mem- pro toplast by strands and is the two contractile vacu - 
brane, which is pierced . ... oles, the red pigment 
by the two cilia. After P ierced b X the two Clha spot, and the two cilia. 
WEST. (fig. 22). After WEST. 
