IN USE AT THE ROYAL BOTANIC GARDEN. 223 
to be preserved relative to the amount of fluid employed. A one 
per cent. solution will preserve plant-structures for a time, but 
ultimately moulds invade the preparation, and this happens 
relatively sooner if any part of the specimen be left exposed 
above the surface of the fluid. A point of importance is the 
deterioration of the fluid which in the course of time appears to 
a certain extent to take place. Formaldehyde gas is extremely 
volatile, and unless the jars containing the specimens are carefully 
sealed a weakening of the solution undoubtedly follows. From 
my experiments it appears that a deterioration may result— 
firstly, in consequence of the volatile nature of the formaldehyde 
gas, and secondly, as a result of changes and decompositions 
which it would seem take place in the presence of organic sub- 
stances in the fluid itself. This being so, it is not surprising 
that the weaker solutions after a time permit the growth of 
moulds. 
A note of interest in connection with the presence of acid 
substances in formalin is contributed by M. Trillat,! who points 
out that commercial formalin may contain as impurities acetic 
acid, formic acid, and pyroligneous products. 
Formalin does not very readily wet the surface of plants, and 
penetration of the specimen by the liquid I have found to be in 
consequence comparatively slow. Until penetration is complete, 
and even for some time after, plants may retain to a certain 
extent their natural colours. The results of my experiments in 
this direction are as follows :— 
Formalin for Preservation of Natural Colours. 
The red, yellow, and blue colours of flowers are better retained 
than they are in most other media; but the retention is not 
permanent. Red and yellow colours are retained longer than 
blue, but even red—the colour which has proved most permanent 
—ultimately fades or gives place to a brown if the jar containing 
the specimen is exposed to the light. | 
Formalin does not appear to extract chlorophyll, neither does 
it preserve the green colour, but exposed even to diffused light 
the chlorophyll is decomposed and the specimen assumes a dull 
brownish colour, or may, finally, be bleached quite white. 
‘Journ. de Pharm. (5), xxix., p- 537: 
