28 HANDBOOK OF SEA-WEEDS. 



clean fresh water, dried between coarse towels, and pressed and 

 dried in the same way as flowering plants. A collection of 

 Algae may be fastened on sheets of paper of the usual herbarium 

 size and kept in a cabinet or portfolios, or attached to the 

 leaves of an album. For scientific purposes, however, the latter 

 is the least convenient way. 



There are few objects more beautiful than many of the 

 sea-weeds when well preserved ; but the filiform species, 

 especially those of the first sub-order, do not retain their 

 distinguishing characters when pressed as has been described. 

 Portions of these, however, as well as sections of stems and 

 fruit, may be usefully dried on small squares of thin mica, 

 for subsequent microscopic examination, or they may be 

 mounted on the ordinary microscope slides. This is the 

 only course possible with Desmids and Diatoms. The former 

 are to be sought in shallow pools, especially in open boggy 

 moors. The larger species commonly lie in a thin gelatinous 

 stratum at the bottom of the pools, and by gently passing the 

 fingers under them they will be caused to rise towards the sur- 

 face, when they can be lifted with a scoop. Other species form 

 a greenish or dirty cloud on the stems and leaves of other 

 aquatic plants, and by stripping the plant between the fingers 

 these also may be similarly detached and secured. If they are 

 much diffused through the water, they may be separated by 

 straining through linen ; and this is a very common way of pro- 

 curing them. Living Diatoms are found on aquatic plants, on 

 rocks and stones, under water or on mud, presenting themselves 

 as coloured fringes, cushion-like tufts, or filmy strata. In colour 

 the masses vary from a yellowish brown to almost black. They 

 are difficult, both when living and dead, to separate from foreign 

 matter ; but repeated washings are effectual in both cases, and, 

 for the living ones, their tendency to move towards the light may 

 also be taken advantage of. When only the shells are wanted 

 for mounting, the cell contents are removed by means of hydro- 

 chloric and nitric acid. The most satisfactory medium for pre- 

 serving fresh Desmids and Diatoms is distilled water, and if the 

 water is saturated with camphor, or has dissolved in it a grain 

 of alum and a grain of bay salt to an ounce cf water, confervoid 

 growths will be prevented. For larger preparations of Algce, 

 Thwaites' fluid is strongly recommended. This is made by 

 adding to one part of rectified spirit as many drops of creasote 

 as will saturate it, and then gradually mixing with it in a pestle 

 and mortar some prepared chalk, with sixteen parts of water ; 

 an equal quantity of water saturated with camphor is then to be 



