232 PHARMACEUTICAL BOTANY 
produced by conjugation, by egg cell and sperm cell union (oospores) 
oogamous reproduction. Green algae live mostly in fresh water. 
Some live in brackish water and a few in the sea. Some are asso¬ 
ciated with fungi to form lichens. 
1. Order Protococcales or One-celled Green Algae. —This order 
contains nearly all of the one-celled green algae excepting the diatoms 
and desmids. 
Family Pleurococcaceae. — PleiCrococcus vulgaris is a one-celled 
green alga, millions of which, living together in colonial fashion, con¬ 
stitute the so-called “green stain” that is common on the north 
sides of tree trunks, stone walls and fences. Each organism con¬ 
sists of a protoplast surrounded by a cell wall of cellulose. The 
protoplast contains a chromatophore, cytoplasm and nucleus. 
Reproduction takes place by the protoplast dividing into two equal 
parts and laying down a cell wall forming two daughter-protoplasts. 
These may again divide to form four granddaughter-protoplasts. 
Still another division may occur as a result of which eight great- 
granddaughter-protoplasts are formed wtich frequently adhere to 
one another forming colonies. 
2. Order Volvocales. —This order comprises free-swimming 
aquatic forms whose vegetative cells are bi-ciliated, green, more or 
less spherical or compressed. Some of the organisms like Sphcerella 
and Chlamydomonas consist of single cells bearing a pair of cilia, 
while others like Pandorina , Eudorina and Volvox show varying de¬ 
grees of colony formation. Reproduction sexual or asexual. 
Volvox globator, a typical representative of this order, is found in 
fresh water pools as a tiny, hollow, spherical, green colony about 
}io to }io of an inch in diameter. When examined under the 
microscope (Fig. 112), it is found to consist of hundreds of green, 
more or less spherical cells, united by fine strands of cytoplasm 
(protoplasmic bridges), the whole being*enveloped by a gelatinous 
sheath. The peripheral cells are provided with cilia, in order that 
the colony may rotate and roll through the water. In a young 
colony, all of the cells are alike, each consisting of a mucilaginous- 
like cell-wall enclosing cytoplasm, a nucleus, a chloroplast and often 
a red pigment spot. In a mature colony, however, throughout the 
greater part of its existence, two kinds of cells may be discerned: 
