COLOUR-RE ACTION. 
3 
Perhaps in no department of biology is colour-reaction of 
more practical use clian in the study of the Lichens. 
Nylander was one of the first to call attention to its value, 
but the principle had many a battle and many a struggle 
before it was accepted, and even now it is looked upon rather 
sceptically by some. Dr. Lauder Lindsay, having tried many 
hundreds of experiments, came to the conclusion that “ there 
was nothing in it,” as may be seen from the following extract 
from one of his papers on this subject:— 
“ These reactions occur of every degree of intensity, from 
the faintest and most obscure to the most brilliant and 
deepest. But in a far larger proportion of cases no reaction 
is exhibited at all; and in species in which it is usually 
developed it is capricious in the extreme—its development 
being apparently determined by the most trivial circumstances 
affecting (e.g.) the freshness or other condition on the one 
hand, and the reagent on the other. By reason of this 
extreme inconstancy of result, chemical characters cannot, 
I think, be relied on as furnishing a means of determining 
species. Certainly they have never afforded me any aid in 
this respect.” # 
But, fortunately, Dr. Lauder Lindsay recorded his experi¬ 
ments, and so they have been useful to others, although not 
to himself. And after many careful experiments, it was 
established that, given the same conditions, the same results 
might be looked for, so that after long waiting, colour-reaction 
has at last become generally accepted as a Lichen test. Thus 
Leighton in England, Nylander on the Continent, and many 
others, accept the principle, and use it largely and success¬ 
fully in their work. 
There are three principal reagents used:— 
Iodine ... ... =1. generally giving blue reactions. 
Hypochlorite of Lime = C. ,, ,, red ,, 
Hydrate of Potash = K. ,, ,, yellow ,, 
Iodine (as is well known in chemistry) possesses the 
property of turning starch and amyloid bodies blue, and so is 
generally applied to sections of the apotliecia, when the asci 
are transformed from their plain semi-transparency to a 
delicate blue, thus rendering them at once visible, and their 
forms and positions may be easily ascertained. A reference 
to figure 1, plate 1, may render this more easily understood. 
The figure represents a section of part of an apothecium of 
Pertusana communis x 150, which when first cut is colourless, 
* Transactions Bot. Society, Edinburgh, for 1869, p. 84. 
