922 SUMMARY OF CURRENT RESEARCHES RELATING TO 



polarized ligtt, and a selenite film. A hand-magnifier is sufficient to 

 show that fir needles are ornamented with rows of white glistening 

 spots. In these the stomata of the plant are situated. Their action 

 upon polarized light is very beautiful, and the changes obtainable by 

 rotating the prisms very striking. Very elegant patterns that would 

 be popular for ladies' dresses, window-curtains, &c., readily appear. 

 So far as the writer knows, these pine needles have been generally 

 neglected by microscopists." 



Cleaning Diatoms.* — J. Y. Bergen, jun., finds the following 

 method works well : 



The diatoms are to be freed as far as possible from water, by 

 decanting it off. Then covered with a liberal quantity of pure con- 

 centrated sulj)huric acid, which is heated to boiling in a good 

 porcelain evaporating dish. Continue the heating till the white fumes 

 of sulphuric acid begin to escape freely, and then, while still over the 

 lamp, add potassium nitrate (saltpetre) in bits the size of a pea, 

 waiting after each addition till the eficrvescence ceases before adding 

 more. Continue till the whole mass in the dish is white or light 

 yellow. This will not usually take more than five minutes. Then 

 wash the cleaned diatoms with successive portions of distilled water 

 as usual. 



Preparation of Fresh-water Algae for the Herbarium.t— P. Eichter 

 recommends that specimens of fresh-water algfe intended for the 

 herbarium should be first of all placed on thin glass, or better upon 

 mica, taking care that they dry as quickly as possible, in order that 

 decay may not set in. When moistened for observation under the 

 Microscope, as little water as possible should be used, and the excess 

 removed as completely as possible by blotting-paper. They must 

 often also be protected by a second layer of mica, which is preferable 

 either to glass or paper. The mica can be readily split under water, 

 but should not be too thin. To replace waste, which will necessarily 

 take place with each moistening for observation, a quantity of the 

 algfe should also simply be dried upon paper ; and for the larger 

 kinds this alone is necessary. Unicellular algre which float free in 

 the water, require no special treatment ; they usually dry quickly on 

 paper. For unicellular or filamentous gelatinous algte, such as the 

 Oscillatoriea3, it is usual to employ stearin-paper, in order to be able 

 to subject them to slight pressure; but it has the disadvantage of 

 keeping the specimens moist for some days, so that decay sets in. 

 Eichter finds the purpose answered better by ordinary yellow straw- 

 paper with either smooth or rough surface ; layers of blotting-paper 

 may be placed between the straw-paper to dry it, and the whole sub- 

 jected to slight pressure; the blotting-paj)er should be changed as 

 often as possible ; the first change may be after half an hour. If the 

 alga sticks to the straw-paper, it can readily be detached by moisten- 

 ing. Chocolate-coloured cellulose-paper answers the same purpose 

 as the straw-paper. 



* Araer. Mon. Micr. Journ., iv. (1883) p. 198. 

 t Hedwigia, xxii. (1883) pp. 97-100. 



