218 ELEMENTS OF BOTANY 
275. Microscopical Examination of Pleurococcus. — Scrape a minute 
quantity of Pleurococcus from a specimen on bark, place it in a drop 
of water on a slide, distributing it slightly in the water, lay on it a 
cover-glass, and examine with a power of 200 or more diameters. 
Sketch with the camera lucida one of the largest cells, some of inter- 
mediate size, and one of the smallest, beside 
several divisions of the stage micrometer. 
Note the clearly defined cell-wall of cellulose, 
enclosing the protoplasmic contents, usually 
green throughout. Do any cells show a nucleus 
like that in Fig. 153 ? 
Test the cells with iodine 
solution for starch. 
Note that in reproduction 
the cell-conteuts in many in- 
dividuals has divided into two 
parts, which become separated 
from each other by a cellulose 
partition. Each of these 
again divides, and the process 
continues until thirty-two or 4, aspherical cell of the still form; B,a 
motile cell with its protoplasm enclosed 
in a loose cell-wall and provided with 
two cilia. 
A 
Fie. 153. Two Cells of Spherrella. 
(Greatly magnified.) 
more cells may be found in 
one mass, or they may fall 
apart at an earlier stage. 
276. Nutrition of Pleurococcus.— Plewrococcus can flourish only with 
an abundance of light and moisture. In daylight it can absorb carbon 
dioxide and fix carbon (giving off the oxygen at the same time in the 
form of bubbles) and can assinilate mineral substances. Itis a capital 
example of an individual cell capable of independent existence. 
277. Motile Forms. 
Spheerclla, often known as Hematoceus (Fig. 153), is a better object 
for study but more difficult to collect than Pleurococcus. It may some- 
times he found in water of stagnant pools, particularly those which con- 
tain the drainage of barnyards or manure-heaps, in mud at the bottom 
No motile form is known in Plewrococcus. 
of eaves-troughs, in barrels containing rain-water, or in water standing 
in cavities in logs or stumps. Its presence is indicated by a greenish 
or sometimes by a reddish color. Ut is sometimes found in an actively 
swimming condition, in which case each cell is called a zodspore. 
