Vol. 2] Gardner.— Cytological Studies in Cyanophyceae. 241 



the plants is poured off. This process is repeated until the coarse, 

 heavy material is removed. Graniteware pans have been found 

 to be most convenient to hold the plants thus segregated, since 

 they are opaque. This material is placed in the shade and al- 

 lowed to settle to the bottom of the vessel, whereupon it will crawl 

 to the center in a mass. Any fine debris remaining on the surface 

 is disposed of by floating a sheet of paper on the surface and re- 

 moving paper and debris together. When placed in direct sun- 

 light oxygen is given off, and, collecting into bubbles, is held in 

 the meshes of the trichomes, so that the whole mass of plants with 

 some fine debris is raised to the surface of the water. From the 

 margin of this mass the plants crawl out and form a thin, clean 

 layer on the surface of the water. This thin, floating layer, which 

 forms a fringe around the mass of material, is carefully trimmed 

 away with a pair of sharp scissors, and placed in a vial with 

 water. In order to get the filaments thus trimmed off into a 

 small mass for embedding, they are repeatedly sucked into and 

 forced out of a pipette until thoroughly broken up. On standing 

 for a few hours in the shade, they will be found to have crawled 

 together again into a single mass, and in this condition may be 

 killed and embedded in paraffin for sectioning. 



If an abundance of material is at hand, as compared with 

 the amount of soil and debris, one may, instead of bringing it 

 into the direct sunlight, allow it to remain in the shade on the 

 bottom of the vessel until the plants have crawled out of and 

 formed a thick layer on the debris, from which the clean top lay- 

 ers may be removed with fine forceps, if due care is exercised. 



Some of the small species are found scattered among fine de-- 

 bris. In order to get them clean, centrifuging may be resorted 

 to. This separates the debris and leaves the plants still scattered 

 through the water, which may now be decanted and collected by 

 filtration. The best filter paper I know of for this purpose is 

 Schleicher & Schiill's No. 575. This is firm, smooth, and strong, 

 and may be subjected to considerable force in a filter-pump. 

 Chamois skin may also be used for this purpose. If desired, the 

 material may now be taken out and killed, then washed by means 

 of the above apparatus, preparatory to embedding. This is a 

 practical way to wash any form, for it is otherwise difficult to 



