222 INTRODUCTION TO BOTANY 
plants, placed side by side, to make a row that would reach 
across the unsharpened end of an ordinary lead pencil. How 
does Plewrococcus compare in size with average bacteria ? 
The spherical plants consist each of a small mass of living 
material, or protoplasm, surrounded by a cell wall. The pro- 
toplasm is so thoroughly colored by chlorophyll that usually it 
is not easy to see the centrally placed nucleus (fig. 174). Some- 
times in these plants special parts 
of the protoplasm hold the chloro- 
phy, and each of these is known 
as a chloroplast, which means 
“a green body,” or a chlorophyll- 
containing body. Parts of the pro- 
toplasm that surrounds the nucleus 
and the chloroplasts are granular 
and are called cytoplasm. Some of 
the internal space of this one-celled 
Fic. 174. Green slime ; 
(Pleurococcus) plant may be occupied by one or 
u, single plants showing cell wall, more vacuoles, which are regions 
granular cytoplasm, and nucleus; surrounded by cytoplasm and filled 
b, plants in process of reproduc- * Bie ‘ 
tion by division, or fission; c and with air or water. 
d, further divisions sometimes re- 206. The food of Pleurococcus. 
sulting in formation of colonies of 
plants. Greatly enlarged The bark or other substance upon 
which Pleurococcus grows is often 
sufficiently moist to provide it with water. Rains and dew sup- 
ply water intermittently. When dry, the plants remain dormant 
until conditions again become favorable. Carbon dioxide (and 
possibly some moisture) may be absorbed directly from the air, 
and with carbon dioxide and water, and favorable temperature 
and light, Pleurococcus plants may carry on photosynthesis, 
thus making their own foods. Heat, cold, and extreme drought 
are some of the severe conditions which this plant must be 
able to resist in order to live. When plants from any of these 
extreme conditions are placed in favorable moisture, tempera- 
ture, and light, they become bright green within a few hours, 
showing that they are manufacturing foods. 
