160 APPENDIX ON PPtACTICAL WORK. 



by placing the sections, as cut, in a watch-glass holding the reagent, 

 transferring after a time to dilute glycerine. Keagents 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. Iodine colours protoplasm and 

 sieve-tube slime brownish yellow, cuticularized and lignined 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 acid 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 ios. 6d. a set of fifteen 

 permanent slides, illustrating the chief points, from Mr. Arthur Shrubbs, 

 Cambridge. 



IV. Physiology. 



i. Plant Food. — Germinated beans, grains of Indian-corn, &c, will 

 nourish in &food solution containing the essential elements (p. 10), pro- 

 vided air and light have access. Such a food solution may conveniently 

 consist of — i 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. 



