INTRODUCTION. 5 



a few drops of the acid with the water, until the latter is very decidedly impreg- 

 nated with it, as indicated by the senses of smell and taste. 



Almost all species of algae which arc firm and semi-cartilaginous, or almost 

 woody in consistency, are best preserved by simply drying them, and keeping them 

 in the ordinary manner for small plants. The fresh-water alga; wliich bear this 

 treatment well belong to the Phycochromojihycea', such as the Nostocs, Scytonema, 

 &c., the true confervas not enduring such treatment at all. When dried plants 

 are to be studied, fragments of them should be soaked for a few minutes in warm, 

 or for a longer time in cold water. 



The only satisfactory way that algoe can be finally prepared for the cabinet is by 

 mounting them whole or in portions, according to size, for the microscope. Of the 

 best methods of doing this, the present is hardly the time to speak; but a word as 

 to the way of cleaning them will not be out of place. Many of them, especially 

 the larger filamentous ones, may be washed by holding them fast upon an ordinary 

 microscope slide, with a bent needle or a pair of forceps, and allowing water to 

 flow or slop over them freely, whilst they are rubbed with a stiffish camel's-hair 

 pencil or brush. In other cases, the best plan is to put a mass of the specimens in 

 a bottle half full of water, and shake the whole violently; drawing ofi" the water 

 from tlie plants in some way, and repeating the process with fresh additions of 

 water, until the plants are well scoured. At first sight, this process would seem 

 exceedingly rough, and liable to spoil the specimens, but I have never seen bad 

 results from it, at least when practised with judgment. The water seems so to 

 envelop and protect the little plants that they are not injured. 



After all, in many instances it appears impossible to clean these algae without 

 utterly ruining and destroying them — the dirt, often seeming to be almost an inte- 

 grant portion of them ; so that he who despises and rejects mounted specimens, 

 simply because they are dirty and unsightly, will often reject that which, scienti- 

 fically speaking, is most valuable and attractive. 



In finally mounting these plants, the only proper way is to place them in some 

 preservative solution within a cell on a slide. After trial of solution of acetate of 

 alumina and various other preservative fluids, I have settled upon a very weak 

 solution of carbolic acid, as the best possible liquid to mount these plants in. 

 Acetate of alumina would be very satisfactory were it not for the very great 

 tendency of the solution to deposit minute granules, and thus spoil the specimens. 

 As every one knows, the great difliculty in preserving microscopic objects in the 

 moist way is the perverse tendency of the cells to leak, and consequently slowly to 

 allow entrance to the air and spoil the specimen. 



As I have frequently found to my great chagrin, the fact that a slide has re- 

 mained unchanged for six months, or even a year, is no guarantee that it will remain 

 so indefinitely. It becomes, therefore, exceedingly important to find some way of 

 putting up microscopic objects that can be relied on for their preservation. Where 

 carbolated glycerine jelly or Canada balsam can be used, the solid coating which 

 they form around the specimens constitutes the best known protection. Except in 

 the case of the diatoms, however, these substances so shrivel and distort the fresh- 

 water alga? immersed in them as to utterly ruin them. I lost so many specimens 



