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aquatic plants. The common Hornwort, Ceratophylum demen- 

 sum^ is often thickly incrusted with Synedrce, Melosirce, &c., so 

 that it is of a brownish color. Marine plants are also covered in 

 the same manner ; thus, I have had Bryopis completely covered 

 with Melosira Borreri and Cocconeis SG^tellum ; the first species 

 being again the support for Podosphenia and Synedra. Ectocar- 

 pus is often so covered with Synedra^ and the freshwater Con- 

 fervcB have in general so many Diatoms growing attached to 

 them, that I have in this way collected several ounces of Synedra 

 radians. On rocks and sticks, more especially in running water, 

 are to be found the filamentous and frondose species. In the 

 month of April last, I found in the fountain in Washington 

 Square, New York, in which the water had been kept running all 

 through the winter, a large quantity of Fragilaria capucina asso- 

 ciated with a few other species, and incrusting the iron tube of 

 the fountain. The Fragilaria, from growing in rather violently 

 running water, was extremely tenacious in the adherence of its 

 frustules one to the other. Some freshwater species are to be 

 found floating on the surface, but this is not as often the case as 

 with the brackish. The plants bearing the Diatoms may be agi- 

 tated in clear water and the species allowed to settle. The water 

 used should be from the same locality as the Diatoms, or, if from 

 any other, be carefully filtered through chemists' filtering paper. 

 This precaution will prevent the introductioo of any extraneous 

 species which it would be impossible afterward to remove, and 

 prove extremely puzzling, as I had experienced until I found out 

 this method of obviating it. Writers in general recommend the 

 use of distilled water, but the filtered article answers every pur- 

 pose, and is procured by a much easier and expeditious process. 

 The general appearance of Diatoms when floating, is of a reddish- 

 fawn colored mass of a seeming porous nature, but when they are 

 in small quantity they appear only as a stain on the water, and 

 when attached to floating confervae the brown of the Diatoms is 

 masked by the green of the confervse. A pond or stream may be 

 known as likely to yield Diatoms, from its having growing in it 

 much vegetation of a larger size. In general, quiet ponds, or 

 such as have but slow streams running into and emptying out of 

 them, will be more likely to reward the searcher than briskly 

 running streams, in which the Diatoms are loosened from their 



