1913.] NATURAL SCIENCES OF PHILADELPHIA. 581 



tioned illustrious amateurs, both living and dead, whose work has 

 added greatly to our knowledge of nature. 



The abundance of diatoms in clear waters was indicated, and ap- 

 paratus useful in making collections were exhibited and described. 

 Methods of separating diatoms into pure condition were explained 

 in outline, and those depending on motile activity were emphasized 

 as preferable in many cases to chemical treatments and laborious 

 •decantations. Sedentary forms, such as Synedra, growing on algae, etc., 

 may often be separated by exposing the gathering to sunlight, when 

 the diatoms fall off the buoyant mass and deposit as a perfectly 

 clean layer on the bottom of the bottle. Filamentous forms may 

 usually be cleaned by gentle agitation in distilled water, exposure 

 to sunlight causing flotation, and by other similar means. Motile 

 forms, if in gelatinous aggregates, as Cijmbella, Gotnphonema, are put 

 into a Petri dish with distilled water and permitted to wander out of 

 the unpromising aggregate into thin films or pure groupings on the 

 bottom of the vessel. Unequal lighting of the dish will generally 

 cause preponderant groupings toward the light. The clean frustules 

 are transferred to watch-glasses of distilled water, working with a 

 capillary pipette and low-power binocular microscope. Tenacious 

 or leathery layers of Nitzschia, on stones in rapid waters, are cut off 

 with a knife, and after freeing from detachable mud are left in a 

 small flat bottle of distilled water for 24 hours. The diatoms expand 

 on the upright glass walls, especially upon the lighted side, into thin, 

 coherent films of great purity, detachable with a sharp needle or 

 similar instrument. Larger Naviculse not coherent, but aggregated 

 in patches on the bottom of a spring, are lifted with as little mud as 

 possible, and separated from organic and inorganic flocculence in 

 the same bottle; and a separation in course of Pinnularia, was 

 exhibited, in which the large frustules could be seen, with the aid of 

 a pocket lens, expanding on the glass. 



Distilled water, if well aerated and uncontaminated with metals, 

 especially copper, seems to stimulate the desired activities. The 

 diatoms having been segregated by such means, they are transferred 

 with a capillary pipette to a clean cover-glass, dried and burned to 

 whiteness. The glass is supported on a thin piece of platinum, 

 which in turn rests on a piece of fireclay ground flat. The fireclay 

 is heated to bright redness with a gas burner, the platinum showing 

 only a faint glow. In about fifteen minutes the frustules are free 

 from organic matter, and the mount may be made in the usual way 

 with Canada balsam or styrax. 



The biological method of cleaning, apart from its facility in handling 

 sparse or unpromising material, gives opportunity for interesting 

 observations on the living diatoms. 



On Diatoms of Philadelphia. — Mr, Charles S. Boyer described 

 the diatomaceous fiora of Philadelphia, stating that he was able to 

 add seventy-one names to the catalogue of species heretofore re- 



