93 



HARDWICKE'S SCIENCE-GOSSIP. 



at Rome), cloisters, and interiors, and views of bare 

 trees. 



Whether the foregoing explanation accounts for 

 the phenomenon or not, I think there can be no 

 doubt that the pleasure of quietly and thoughtfully- 

 studying good drawings will be very greatly en- 

 hanced by the method I am advocating, viz., that of 

 looking at them with one eye only. 



I may mention to those who wish to try the 

 experiment for themselves with the best effect, that 

 Mr. Newman, of Soho-square, has a simple, useful, 

 "handy " little instrument for the purpose, which 

 greatly facilitates the process. 



Thurlozc, Clapham, S.W. 



ON PRESERVING AND MOUNTING 

 FRESH-WATER ALG^. 



TTAVING had considerable experience in this 

 -^-^ matter, and having mounted many hundreds 

 of slides which have retained much of their original 

 beauty for many years, I may perhaps be able to 

 give a useful hint or two to your correspondent 

 interested in the subject. I have specimens 

 mounted as early as 1851 which, though they have 

 lost their green colour, still show the natural dis- 

 position of the endochrome, retain their external 

 form unimpaired, and show no signs of intrusion of 

 the varnish. The bulk of my slides are five or six 

 years old, and the percentage of those which show 

 any signs of "running in," or of evaporation of the 

 liquid, is very trifling. 



Such as are defective are nearly all my earlier 

 attempts, and I firmly believe that slides mounted 

 according to the plan I now adopt are practically 

 permanent. Let us divide the subject into four 

 heads ; viz., forming the cells, fluid to be used, 

 introduction of the plant, and sealing the cells. 

 My plan is as follows : — 



1st. The Cell.— 'For most Algse, including the 

 Desmidiaceae, a ring of thin gold size, spun by means 

 of a " tm-ntable." 



This should not be narrow— J inch is not too 

 much ; it should be either left to harden for several 

 months or baked for a few hours in a slow oven. 



Tor thicker Algee, as Batrachosperms, Brapar- 

 naUiai, &c., I prefer block-tin rings, which should 

 be cemented to the glass by marine glue. 



2ud. The Fluid. — I have tried nostrums innumer- 

 able without finding any which preserves the colour 

 of these plants, and have come to the conclusion 

 that we must be content if we can keep the endo- 

 chrome in its natural form, sacrificing its colour. 



Now if the medium be denser than the water 

 with which the plant is filled, the endochrome is 

 forced into the middle of the cell in a shapeless 

 mass. It is essential to avoid this condition ; and 



after many 'experiments, I have adopted distilled 

 water, slightly camphorated to prevent growth of 

 fungi in the cell. If this medium be used, the 

 endochrome usually retains its natural form and 

 position. 



3rd. Introduction oftlie Object. — Dr. Wood's mode 

 of scouring the plants is inapplicable to any species 

 with which I am acquainted. My own experience 

 is that the specimen should be raised from the 

 water in which it grows with as little disturbance 

 as possible, placed at once in a drop of the medium 

 in the cell, and, if necessary, slightly arranged by 

 means of two needles. (The Desmidiacese require 

 special treatment to obtain them quite clean, which 

 I shall be happy to describe in another paper if 

 desired, but which I pass for the present.) 



4th. Sealing the Cell. — The most important part 

 of the business. 



The great secret of securing permanency is this : 

 — Immediately before placing the object in the cell, 

 put the latter on the turntable, and moisten the 

 ring with the least possible dressing of fresh gold- 

 size ; touch the edge of the glass cover for about 

 one-sixteenth of an inch inwards with the same 

 substance. 



Then lower the cover on to the cell. If there be 

 a superfluity of the liquid, the fresh gold-size resists 

 its escape, and the cover floats, as it were, on the 

 medium. A gentle pressure then forces out the 

 surplus liquid, and the last portions may be drawn 

 out by a fragment of blotting-paper. No air enters, 

 yet the medium is sucked out by the paper until 

 the pressure of the air holds the cover on so tightly 

 that it can scarcely be pushed on one side. The 

 two surfaces of gold-size amalgamate without a 

 particle of water remaining between or, in other 

 words, neither cover nor cell is ever wetted. 



Finally, two or three successive coats of gold- 

 size are run round the edge of the cover at intervals 

 of a few days, and the whole is secure. For a finish, 

 I use a coating of copal-varnish, in which vermil- 

 ion has been rubbed up with a palette knife ; others 

 prefer a similar preparation of white lead. It is 

 most important to keep the slides flat in the cabinet ; 

 I believe the most carefully prepared specimen will 

 give way in time if kept vertically.' 



While writing on this subject, may I remark that 

 it is a great pity that this most interesting but 

 complicated tribe of plants does not find some 

 bibliographer who has time and ability to collate 

 and reconcile the almost innumerable descriptions of 

 genera and species now scattered through the works 

 and papers of Kiitzing, Braun, Thurct, Hassal, and 

 a score of other observers at home and abroad, at 

 present forming a heterogeneous mass of data, 

 accessible to few, intelligible to fewer still, and 

 requiring the patient labour of a master -hand 

 during many years to reduce them to a harmonious 

 scientific whole. A. W. Wills. 



