220 ELEMENTS OF BOTANY. 
which Protococcus is growing should be put in a shallow dish, loosely 
covered with a pane of glass, to prevent drying up, and set in a sunny 
place. 
267. Microscopical Examination of Protococcus.2 — Place a drop of 
water containing Protococcus on a slide, lay on it a cover-glass, and 
examine with a power of 200 or more diameters. Sketch with the 
camera lucida several divisions of the stage micrometer alongside of one 
of the largest cells, some of intermediate size, and one of the smallest. 
Note the clearly defined cell wall, of cellulose, enclosing the proto- 
plasmic contents, usually green throughout, sometimes red throughout, 
sometimes of both colors. Do any cells show a nucleus like that in 
Fig. 102 ¢, f, g, &, t? 
Test the cells with iodine for 
starch. 
4 Note that the cell-contents in 
2 many individuals has divided into 
e two parts, which become separ- 
D E 
ated from each other by a cellulose 
partition. The mode of division 
Fig. 190.—A Unicellular Plant (Palmo- 18 not unlike that shown in Fig. 
glza). (Greatly magnified.) 190, but the cells in that figure 
A, a single cell in its ordinary condition, have not the distinct cell wall 
consisting of a mass of protoplasm col- that Protococcus has, while they 
ored green by chlorophyll and sur- are covered with a layer of gel- 
rounded by a transparent gelatinous atinous material not found in 
envelope; B, the cell-contents elongating Atensa'e 
preparatory to multiplying by fission into Protococcus. After the division 
two portions; C, the process carried a Of a Protococcus cell into two por- 
step farther; D, the two cells quite dis- tions, each may at once constitute 
tinct, but surrounded by a common a new cell, with a complete sac 
gelatinous envelope; £, each of the new : : 
of cellulose surrounding it, or 
cells much enlarged and forming a 
gelatinous envelope of its own. each of the halves formed by the 
first sub-division may break up 
into halves again before the cell wall is formed around the new portions. 
A B C 
1If it is found impracticable to collect Protococcus for examination, the green, 
powdery Pleurococcus found everywhere on the shady sides of trees or unpainted 
fences will answer very well to show unicellular plants containing chlorophyll, and 
to illustrate multiplication by cell-division. 
2 Slides permanently mounted and purchasable of the dealers (see Appendix C) 
will answer for most of the microscopical examinations almost as well as the living 
cells. 
3 See Clark’s Practical Methods in Microscopy, pp. 31-35. 
