28 SOUTH AFRICAN BOTANY 
contain? What purpose does it serve in the economy of the 
plant ? , 
5. What is cellulose? How would you test whether cellulose 
was present ina plant tissue or not? What modifications of 
cellulose are often found in plants? Describe the character- 
istics of these modifications. 
6. Of what substances do the crystals found in plant cells 
usually consist ? Describe the appearance of any crystals you 
may have seen during a microscopic examination of sections 
of plant tissue. Why are these crystals formed by the plant ? 
7. Describe any experiments you may have performed to 
illustrate the nature and properties of chlorophyll. Under 
what conditions is it found, and how does it occur in the plant ? 
8. What is meant by cell sap? How does it oceur, what are 
ts commonest ingredients, and how can these be recognized ? 
9. How does sclerenchyma differ from parenchyma? Men. 
tion some places where these tissues are found. Name some 
of their uses. 
FURTHER PRACTICAL EXERCISES ON CHAPTER IT. 
6. Mount in a drop of water hairs from a stamen of Trade- 
scantia or from stem of cucumber. Observe streaming meove- 
ment of the protoplasm. Run ina few drops of chlor-zinc-iodide 
and note staining of the cell wall. 
7. Soavk hairs from cotton seed in Schultz’s solution, mount in 
glycerine and water, and note that ccll-walls made of cellulose 
are stained purple. 
8. Cut thin sections of wood of a match, stain with aniline 
sulphate, note bright yellow colour. Examine sections under 
microscope, and note thickened cell walls. 
9. Cut longitudinal sections of any young stem, and try to find 
annular, spiral, and pitted vessels, 
10. Cut longitudinal sections of the stem of cucumber, and 
examine sieve tubes under low and high powers. 
11. Cut sections of ordinary bottle cork, examine under micro- 
scope. Note thickened walls. Treat sections with potash and 
note yellow stain. . 
12. Cut sections of bean and castor-oil seeds, and stain with 
iodine. Note that starch grains in bean stain purple, alcurine 
grains in castor-oil do not. Examine aleurine grains under high 
power and find the erystalloid and globoid 
Norg.—See p. 209 for Appendix to Chapter IT, 
