THE THALLOPHYTES a5T 
the thallus. These chloroplasts vary considerably in form, being 
_in some cases spiral bands, in others star-shaped, in others like a 
napkin ring, and in others granular. In the chloroplasts of most 
“green algz are pyrenoids, which consist of a central crystalline por- 
tion of protein (aleurone-like) surrounded by a starchy envelope 
of variable magnitude. These are called starch centers and the 
starch is frequently in the form of rounded, or angular grains. 
The nutrition of these algz is autotrophic. ‘There is a defi- 
nite nucleus present, but in the ccenocytic forms the nuclei 
may be many within the confines of the cell wall. The motile 
cells have two (except in Oedogoniacee and by fusion in the 
Vauchertacee) to many cilia, as likewise some of the reproductive 
cells. No cilia occur in the conjugate alge. Reproduction is by_ 
Cell division, the formation of zodspores (motile cells), by zygo- 
spores produced by conjugation, by egg cell and sperm cell union 
(odspores) odgamous reproduction. Green algz live mostly in 
fresh water. Some live in sea water and a few in brackish water. 
Some are associated with fungi to form lichens. . 
1. ORDER PROTOCOCALES OR ONE-CELLED GREEN ALGA.— 
This order contains nearly all of the one-celled green algze 
excepting the diatoms and desmids. It also contains a variety 
of many celled forms, the cells of which are devoid of cilia. 
FamiLty PLEuRococcACEa.—Pleurococcus vulgaris [Fig. 245 (2)] 
is a one-celled green alga, millions of which, living together in 
colonial fashion, constitute the so-called “green stain’ that is 
common on the north sides of tree trunks, stone walls and fences. 
Each organism consists of a protoplast surrounded by a cell wall 
of cellulose. ‘The protoplast contains a chromatophore (capable of 
division into 2 or more chromatophores), 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 granddaugh- 
ter-protoplasts. Still another division may occur as a result of 
which eight great-granddaughter-protoplasts are formed which 
frequently adhere to one another forming colonies. 
2. ORDER VotvocaLes.—This order comprises free-swim- 
ming aquatic forms whose vegetative cells are bi-ciliated, green, 
more or less spherical or compressed. Some of the organisms 
oo 
