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, iirst 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. ]\Iake 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- 

 rird in a little water in a white saucer by aid of a magnifying glass. 

 Jlount 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 aud suhsequent 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 Zi/r/neinn, Mesocarpus, Stigeoclonnim, 

 or Draparnaldia will answer. See Bergen and Davis' Principles of Botany, 

 Chapter XX, Ginn & Company. 



