444 MISCELLANEOUS [Bot. Absts. 



to structure. Visibility may be secured under most favorable conditions of a particle of 

 the order of 5 micromillimetres in diameter, but the resulting images of objects, ranging in 

 size from the limits of resolution to the limits of visibility are not such that any idea of form 

 or condition can be established. It is merely a proof that the objeets exist; other physical 

 tests must be applied to approximately determine their size and state. Therefore the limits 

 of resolution are dependent on the effective numerical aperture of the observing system and 

 the mean wave-length of the illuminant. The limits of resolution of two separate objects 

 may be taken as the absolute limit of resolution for all isolated objects that can be seen and 

 observed as definite entities. The limits of visibility are dependent on the difference of re- 

 fractive index between the object and the medium in which it lies, and on the intensity of 

 the illumination. By detailed description of the ultra microscope it is shown that the ef- 

 fectiveness of the instrument is dependent on the concentration of a great quantity of light 

 on a small area, so that only a few of the particles in the field of view are illuminated. The 

 illumination of particles in depth is controlled to ensure that none above or below the focal 

 plane of the observing objective are brought into view. — Julia Moesel, 



3034. Blunck, Gustav. Verwendung des Glyzerinersatzmittels "Glyzinal" in der Mikro- 

 skopie. [Glycerin substitute "Glyzinal" in microscopy.] Zeitschr. Wiss. Mikrosk. 35: 249- 

 251. 1919. — A commercial product similar in some respects to glycerin, said to be based on 

 a mixture of dipyridinbetain-NaCl and dipyridin-CaCl 2 . Recomended as clearing and pre- 

 serving fluid. — H. G. Barbour. 



3035. Chamberlain, Edward B. A herbarium note. Bryologist 22: 39-40. 1919. — 

 Loose-leaf binders are advised for the preservation of small collections and exsiccatae; the 

 specimen-envelopes are pinned directly to the sheets. — Edward B. Chamberlain. 



3036. Conard, Henry S. Relation of the community to the preservation of wild plants. 

 Rept. Iowa State Hortic. Soc. 53: 385-390. 1918. — Calls attention to the wealth of material 

 among our native plants for park purposes. The Atlantic seashore is gilded with goldenrods 

 like Solidago sempervirens, the salt marshes with Sabbatias, nowhere is greater beauty dis- 

 played than on the hills and prairies of Iowa. — L. H. Pammel. 



3037. Cotjpin, H. Sur le montage de quelques preparations microscopiques. [On the 

 mounting of some microscopic preparations.] Rev. G6n. Bot. 31: 109-114. 1919. — Author re- 

 views objections to the use of the ordinary mounting media for certain objects, and recom- 

 mends several new ones for which excellent results are claimed. Stained sections may be 

 mounted directly from water, alcohol or glycerine in a medium made up as follows: 0.8-1 

 per cent aqueous solution of HgCl 2 , 35 cc; gum arabic, 30 grams; glucose, 10 grams. Filter. 

 Seal mount. — For mounting pieces of epidermis: gum arabic, 10 grams; glucose, 5 grams; 

 water, 10 cc; crystal of thymol or few drops of formol as preservative. — For unicellular algae: 

 0.8-1 per cent aqueous solution of HgCh, 35 cc; glucose, 10 grams; gum arabic, 30 grams; 

 ammoniacal copper chloride, 1 gram. Filter. — For filamentous algae: 0.4 per cent aqueous 

 solution of HgClj., 500 cc; gelose, 5 grams; ammoniacal copper chloride, 1 gram. Boil and 

 cool. Melt a piece on the slide and just before it cools add algae and cover. Seal. — For 

 pollen grains: vaseline oil. — L. W. Sharp. 



3038. Curtiss, C. F. Forest parks and their relation to the rural community. Rept. 

 Iowa State Hortic Soc. 53 : 363-364. 1918. — Suggests that the fee for hunters licenses be util- 

 ized for park purposes and game reserves. — L. H. Pammel. 



3039. Davidson, S. C. Coal from peat. Jour. Amer. Peat Soc. 12: 16. 1919.— British 

 patent covering a method of preparing synthetic coal from peat. — George B. Rigg. 



3040. Georgi, J. Zur Verwendung fiachenmessender Instrumente in der Mikrotechnik. 

 [Surface-measuring instruments in microscopic technique.] Zeitschr. Wiss. Mikrosk. 35: 

 175-1SS. 1919. 



