2OO 



BACTERIA IN RELATION TO PLANT DISEASES. 



Omelianski's Magnesia-Gypsum Blocks for the 

 Cultivation of Nitrifying Organisms. 



One per cent carbonate of magnesia is uni- 

 formly mixed with gypsum and water added to 

 it, stirring until it becomes of the consistency 

 of sour cream, when it is poured upon plate- 

 glass and spread out. As soon as the mass be- 

 comes of a doughy consistency and is ready to 

 harden, it is cut into circular blocks for Petri 

 dishes and into strips for test-tubes. The cir- 

 cular pieces may be cut with a Petri dish of a 

 size a little smaller than the dishes it is intended 

 to use. As soon as the gypsum has hardened 

 thoroughly the blocks are pried loose from the 



plate glass, placed bottom up in the dishes (so 

 as to give a smooth surface), and enough of the 

 above (nitrite) culture-medium added to half 

 cover the block. This is then autoclaved and 

 additional sterile culture-media added from 

 time to time as necessary, being careful not to 

 wet the inoculated surface of the block. The 

 sowings are made on the smooth surface of the 

 block and the dishes are kept in a thermostat at 

 25 to 30 C. Colonies begin to be visible in 

 4 to 5 days. In 10 to 14 days many colonies 

 are 0.25 to 0.50 millimeter in diameter. (Cen- 

 tralb. f. Bakt., 2 Abt., Bd. V, 1899, P- 652.) 



MISCELLANEOUS. 



Distilled Water. 

 (See page 124.) 



Chromic Acid Cleaning Mixture. 



This is made by pouring I gallon or more of 

 concentrated crude sulphuric acid into an equal 

 volume of a saturated aqueous solution of po- 

 tassium bichromate. It should be done in a 

 large enameled iron kettle, the acid being added 

 slowly at intervals, with frequent stirring, so as 

 to keep the mixture below the boiling point. An 

 excess of the sulphuric acid should be avoided. 

 Pure water should be used for dissolving the 

 potassium bichromate, and under no circum- 

 stances should this solution be poured into the 

 acid, since steam might be generated and dan- 

 gerous splutterings occur. The resulting chromic 

 acid is very injurious to the skin and should be 

 used with care. At 15 C. each 10 parts by 

 weight of water will dissolve about I part of the 

 potassium salt. The chromic acid mixture is 

 said to explode violently when brought into con- 

 tact with certain substances, e. g., alcohol, gly- 

 cerin. 



Fluid for Softening Hard Tissues. 



Frequently grains of cereals and other hard 

 tissues may be softened for cutting on the 

 microtome with slant stroke by soaking from 

 3 to 6 months in equal parts of alcohol and 

 glycerin. 



Unguentum resinae. 



(See Bibliog., XVII, 'oo, Bulloch.) 

 Darwin's Wax-Mixture. 



This consists of vaseline 50 parts, beeswax 35 

 parts, melted together. Then stir in of pow- 

 dered resin 15 parts. If a stiffer mixture is de- 



sired, add more wax up to 50 parts (see Darwin 

 & Acton, Plant Physiology, p. 3, foot note). 



Pencils for Writing on Glass. 

 (See page in.) 



Pyrogallol Developer. 



(Much used in Laboratory of Plant Pathol- 

 ogy.) 



1 i) Alkali: 

 Carbonate of potash 



(cryst. )* i l / 2 ounces, or 46.5 grams 



Carbonate of soda 



(cryst.)* 2 ounces, or 62 grams 



Distilled water 12^2 ounces, or 375 cc. 



(2) Pyro : 

 Sulphite of soda 



(cryst.)* 4 ounces, or 124 grams 



Citric acid 60 grains, or 3.9 grams 



Bromide of potash.. 40 grains, or 2.6 grams 



Distilled water 12 1 A ounces, or 375 cc. 



Pyrogallic acid i ounce, or 31 grams 



The pyrogallol should be added last of all, and 

 the nearly filled bottle closed at once. 



For a normal developer take 2 drams of No. i, 

 add 2 drams of No. 2, and make up to 4 ounces 

 with distilled water. Reduce the amount of al- 

 kali to one-fourth dram or less in case of much 

 overexposed plates. In case of exposures likely 

 to exhibit too great contrasts reduce the pyro. 

 Always begin development with one-fourth of 

 the alkali, unless the exposure is known to be 

 correct. Both solutions should be kept in glass- 

 stoppered bottles. 



Bottles containing alkali should have the in- 

 side of the neck and the ground surface of the 

 stopper wiped dry before replacing; then the 

 latter will not stick. 



In case anhydrous salts are employed, use one-half as much. 



