212 ESSENTIALS OF BOTANY 
the ferns, the arrangements for respiration, photosynthesis 
(Sect. 163), and transpiration are very complete. 
The student can obtain a reasonably thorough knowl- 
edge of the lower plants only by a prolonged study of 
many types. It is possible, however, to get some idea 
of their general appearance by a rapid examination of 
some characteristic forms. 
264, Examination of Yeast. Obtain some growing yeast-cells 
from compressed yeast mixed with molasses and water. Put a very 
small drop of the liquid on a slide, cover with a cover-glass, and examine 
with h.p. (high power).!_ Note the apparent size, shape, contents, and 
characteristics of the cells. Each cell is a yeast plant. Their actual 
diameter averages about one three-thousandth of an inch. Lacking 
chlorophyll they are incapable of making food by photosynthesis (Sect. 
163) and live on the substances in which they cause fermentation. 
265. Examination of Pleurococcus. — Collect some of the green 
coating which is usually found on the north sides of tree trunks or 
unpainted fences. Place a few flakes of bark or bits of wood with 
their green covering in a plate, moisten with water, cover with a bell- 
glass, and leave for two or three days in a warm, sunny place. Scrape 
off a minute portion of the green coating, mount in water, and exam- 
ine, first with m.p. (medium power) and then with h.p. (high power). 
Note the single cells and grouped cells. Each cell is a Pleurococcus 
plant. The groups result from cell division, and the plant reproduces 
itself freely in this way. Make a careful drawing to show the shapes 
of isolated cells and of some groups. Pleurococcus contains abundant 
chlorophyll and produces plant food by photosynthesis. 
266. Examination of Cladophora.?—- Study living or preserved mate- 
rial in a little water in a white saucer by aid of a magnifying glass. 
Mount a very small portion in a drop of water on a slide, cover with a 
cover-glass, and examine with m.p. Note the shape of the filaments 
1 Throughout this and subsequent chapters the powers of the microscope 
will be referred to as l.p., m.p., and h.p., meaning respectively low power, 
medium power, and high power (see Appendix II). 
2 Any filamentous green alga such as Zygnema, Mesocarpus, Stigeoclonium, 
or Draparnaldia will answer. See Bergen and Davis’ Principles of Botany, 
Chapter XX, Ginn & Company. 
