28 BRITISH LICHENS. 



acquirement of a knowledge of which is the tax we all have to pay on 

 entering the domain of science. Once acquired, however, they become 

 our greatest aids to study, and lead to a precision of thought which more 

 familiar but ill-defined terms would utterly fail in. Leaving this thought 

 to console the student for his trouble, we will now turn to easier branches 

 of our subject. 



As no man can work without tools, we will here specify the essential 

 appliances required for collecting, preserving, and studying Lichens. 

 These may be classed under two heads— 1st. appliances for collecting ; 

 2nd, those for home study. 



I.— Appliances for Collecting.— A pocket lens, having a focal length 

 of 2in. or 2Jin., which can be obtained from any optician for a shilling. 

 Some prefer having one with three powers, in which case a lin., a 2in., 

 and a 3iu. will be found a convenient combination. The external 

 characters of most species of Lichens can be made out with sufficient 

 precision by the aid of these powers, which is all that is required in field 

 work. The rest must be left for home study. 



A hammer such as Geologists carry, with one end broad enough to use 

 with a chisel. 



A stonemason's chisel, of good temper, for detaching portions of the 

 rock on which the Lichens grow. 



A strong clasp-knife, for removing the bark of trees to which the 

 Lichens attach themselves. 



A leather satchel for carrying specimens. 



An ample supply of paper for folding up specimens. 



II. A'ppliayices for Home Study. — The most important of these is a 



good compound microscope. It does not necessarily follow that a micros- 

 cope suitable for the examination of Lichens should be a very expensive 

 instrument. English and foreign makers now supply for about £5 

 an instrument wh^ch will answer all the purposes of the student; 

 but if his means admit of it, there is no economy in having a poor or 

 imperfect microscope, and the best within reach should be procured. 

 Two powers are essential, one a low power, magnifying fifty times, 

 (linear,) the other magnifying from 350 to 400 times (linear.) With such 

 an instrument all can be done that is required. 



A small knife for cutting thin sections, with a supply of glass slides 

 and covering glasses, should accompany the microscope. 



A glue-pot, with a supply of glue for fastening down specimens on 

 paper, on which to write the names of the species, and the localities 

 where they were gathered, with any other necessary remark. Gum 

 should never be used for this purpose, as many valuable specimens will 

 be lost by being rubbed off in the herbarium. The only specimens that 

 present any difficulty in making secure are such as grow on loose sand or 

 soil, and for these the better plan is to make a pool of dissolved glue on 

 the paper, and place on it the mass of earth while still damp, when the 

 glue, if not too thick, will permeate the whole mass and bind it together. 



