AN INTRODUCTION TO THE STUDY OF LICHENS, Lgeye) 
able value and importance. On account of the chemical elements 
in the thallus, it re-acts in certain colours, or not, on the application 
of these re-agents. This reaction, or non-reaction, is a great help 
in the determination of species. The method of examining the 
apothecium or other organ of the Lichen, is to place the plant on 
the table, then, with the lens to the eye, place the knife on the top 
of the organ about midway, and cut it straight down. Cut down a 
second time close to the first, and thus get out a section as thin as 
you possibly can; place it in the compressor, or upon the glass 
stage of the microscope, moisten it with clean water, and put on a 
thin glass cover. Now you may examine the section, and if you 
have a good cut, you will have all the parts of the apothecium 
before you. You must now observe the colour and form of the 
hypothecium, the character of the paraphyses, with the colour of 
their apices ; also, the shape of the asci, and the number, colour, 
form, and septa of the spores. You may now run in a drop of 
iodine, watch and carefully note the results. After this, run in a drop 
of the hydrate solution, which will annul the action of the iodine— 
consequently it must always be used after it, where both are required. 
This does not generally destroy any natural colour, but it will 
show you, if you have obtained a correct idea of the several points 
just named above. When you have thus examined the apothe- 
cium, and the spermogones if you can find any ; and have likewise 
observed the nature of the gonidial layer, then carefully group the 
outer features of the plant. As well as a mark of carefulness, it is 
a good disciplinary process to write down all the points in examina- 
tion as you go on, both internally and externally ; and, when this 
is complete, turn up the Manual and look for a description of your 
plant, under that family, series, tribe, or sub-tribe, to which you 
have already concluded it belongs. Drawings of the spores, or 
any part of the plants, should be attached to the sheets upon which 
they are mounted, and the whole be arranged together in the 
herbarium, according to their classification. Microscopic slides, 
neatly mounted and finished, illustrating different plants, are very 
useful for reference and instruction. 
The Lichen-herbarium is usually made up according to the taste 
and convenience of the parties concerned. Leighton describes 
his in his Lichen-Flora. If it is intended that the herbarium shall 
follow the order of the system of classification, then the best way 
is, to mount each species and form, upon a separate sheet of 
cartridge paper, cut to a convenient size, and in due order arrange 
so many together, in suitable covers, upon the herbarium shelves. 
Thus, as fresh or new species come, they can be inserted in their 
proper places. 
The Lichen-Flora of Great Britain, at present, comprises 
upwards of 1700 species, forms, and varieties; and, undoubtedly, 
