160 APPENDIX ON PRACTICAL WORK. 
by placing the sections, as cut, in a watch-glass holding the reagent, 
transferring after a time to dilute glycerine. Reagents can also be 
added to a mounted section by placing a small drop on one side of the 
cover-glass, and drawing it under by means of a pointed fragment of 
blotting-paper placed on the other side. odine colours protoplasm and 
sieve-tube slime brownish yellow, cuticularized and lignified cell-walls 
yellow, cellulose pale yellow, and starch blue. Magenta stains generally, 
but colours the protoplasm most deeply. If an object is mounted in 
iodine, and a drop of strong sulphuric acud run under the cover-glass, the 
cellulose walls will be coloured blue. 
Sections can be cleared, i.e., rendered more transparent, by mounting 
in caustic potash solution. This method is especially useful in the case 
of roots. 
In all the preceding cases it is essential to mount the object in a 
very small drop of liquid, just enough to spread out under the cover- 
glass. If too much is taken, the inclined stage (if the field-microscope 
is used) will cause the cover-glass to slide off. 
Students who wish to learn a little vegetable histology, but have no 
time to make their own sections, can obtain for ros. 6d. a set of fifteen 
permanent slides, illustrating the chief points, from Mr. Arthur Shrubbs, 
Cambridge. 
IV. PHyYsmIoLoey. 
1. Plant Food.—Germinated beans, grains of Indian-corn, &c., will 
flourish in a food solution containing the essential elements (p. 10), pro- 
vided air and light have access. Such a food solution may conveniently 
consist of—1 pint distilled water, 86 grains potassium nitrate, 43 grains 
sodium chloride, 43 grains calcium sulphate, 43 grains magnesium sul- 
phate, 43 grains of finely divided calcium phosphate, and a trace of ferric 
chloride. The omission of any constituent will cause the plants to be 
sickly and stunted. The carbon dioxide in the air forms part of plant 
food. See p. 68. 
2. Action of Chlorophyll—Green plants grown in the dark become 
etiolated (p. 68). See also p.67 Oxygen is evolved. See pp. 68-69. 
3. Transpiration.—See p. 69. 
4. Respiration.—The necessity for oxygen is proved by growing plants 
in nitrogen. They sicken and die. A large wide-mouthed bottle is 
one-third filled with germinating peas, and closed with a tightly-fitting 
stopper. After a few hours enough carbon dioxide will have collected 
to put out a burning candle-end lowered into the bottle. 
5. Growth of Pollen-tubes.—See note on p. 114. 
6. Germination.—Beans, &c., can be germinated in sand or sawdust, 
mustard and cress on flannel. They require (a.) water, (b.) access of air 
containing oxygen, (c.) a moderately warm temperature. They do not 
require light, or other food than water, since the cotyledons or endo- 
sperm contain a store of nutriment in the form of reserve materials. 
But when these are used up germination is completed, and food and 
light become essential. 
The growth of shoots from bulbs, corms, and tubers may take place 
under the same conditions as the germination of seed. 
