MICROSCOPIC FORMS OF VEGETABLE LIFE. 305 



the latest will require the higher powers a separation which is attended 

 with great convenience. 1 It sometimes happens that fossilized Diatoms 

 .are so strongly united to each other by Siliceous cement, as not to be 

 separable by ordinary methods; in this case, small lumps of the deposit 

 should be boiled for a short time in a weak Alkaline solution, which will 

 act upon this cement more readily than on the siliceous frustules; and as 

 soon as they are softened so as to crumble to mud, this must be immedi- 

 ately washed in a large quantity of water, and then treated in the usual 

 way. If a very weak alkaline solution does not answer the purpose, a 

 stronger one may then be tried. This method, devised by Prof. Bailey, 

 has been practised by him with much success in various cases. 2 



301. The mode of mounting spcimens of Diatomacece will depend 

 upon the purpose which they are intended to serve. If they can be ob- 

 tained quite fresh, and if it be desired that they should exhibit, as closely 

 as possible the appearance presented by the living plants, they should be 

 put-up in aqueous media ( 206) within Cement-cells ( 211);" but if they 

 are not thus mounted within a short time after they have been gathered, 

 about a tenth-part of alcohol should be added to the water. If it be de- 

 sired to exhibit the stipitate forms in their natural parasitism upon other 

 aquatic plants, the entire mass may be mounted in Deane's Medium or 

 in Glycerine jelly ( 206 h), in a deeper cell; and such a preparation is 

 a very beautiful object for the back-ground illumination. If, on the 

 other hand, the minute structure of the siliceous envelope is the feature 

 to be brought into view, the fresh Diatoms must be boiled in nitric or 

 hydrochloric acid, which must then be poured off (sufficient time being 

 allowed for the deposit of the residue); and the sediment, after being 

 washed, should be boiled in water with a small piece of soap, whereby 

 the Diatoms will be cleansed from the fiocculent matter which they often 

 obstinately retain. 3 After a further washing in pure water, they are to 

 be either mounted in Balsam in the ordinary manner ( 210), or to be 

 .set-up 'dry' on a very thin slide ( 165, 169). In order to obtain a 

 .satisfactory view of their markings, Objectives of very wide angular 

 aperture are required, and all the refinements which have recently been 

 introduced into the methods of Illumination need to be put in practice. 

 (Chaps, in., iv.) It will often be convenient to mount certain particular 

 forms of Diatomacece separately from the general aggregate; but on 

 account of their minuteness, they cannot be selected and removed by the 

 usual means. The larger forms, which may be readily distinguished 

 Tinder a Simple Microscope, may be taken-up by a camel-hair pencil 

 which has been so trimmed as to leave two or three hairs projecting beyond 

 the rest. But the smaller can only be dealt with by a single fine bristle 



1 A somewhat more complicated method of applying the same principle is de- 

 scribed by Mr. Okeden, in the "Quart. Journ. of Microsc. Science," Vol. iii. 

 (1855), p. 158. The Author believes, however, that the method above described 

 will answer every purpose. 



,. P- 



"Practical Directions for collecting, preserving, transporting, preparing, and 

 mounting Diatoms" (New York, 1877), containing Papers by Professors A. Mead 

 Edwards, Christopher Johnson, and Hamilton L. Smith, will be found to contain 

 much useful information. 



! See Prof. H. L. Smith in " Amer. Journ. of Microscopy," Vol. v. (1880), p. 

 257. It is important that the soap should be free from kaolin, silica,or any other 

 insoluble matter. 

 20 



