IN USE AT THE ROYAL BOTANIC GARDEN. 231 
specimen is known to darken in alcohol it is treated before pre- 
servation ; but if placed in alcohol without treatment and subse- 
quently found to need bleaching it is treated by one of the methods 
given under c. It follows that a knowledge before preserving of 
the behaviour in alcohol of any particular specimen is a consider- 
able aid in choosing the best method of procedure. No definite 
rules can be given, but the following statements afford some 
indication of the class of specimen for which bleaching other 
than by alcohol alone will generally be found to be necessary. 
Specimens usually darkening in alcohol are those whose 
tissues contain large quantities of tannin, similarly also those in 
which much resin is present. Thick and leathery leaves and 
leaves with thick cuticles turn brown as a rule in alcohol, as do 
also flowers in- which brown and yellow colours predominate 
White flowers, if fleshy and of a waxy appearance, frequently 
darken; if the petals are thin they commonly bleach well in alcohol. 
Leaves, stems, and other parts, of a light green colour bleach 
white, while those of a darker colour often do not. In the same 
way young tissues bleach better than older ones. Most seedlings 
bleach well, the exceptions being particularly some of the Ranun- 
culacez and seedlings generally with slightly woody roots, for 
instance, palms and members of the Cupuliferz. 
Where I have found it possible to institute a comparison of the 
members of different families, I have found with certain excep- 
tions that the Ranunculaceze and Cupuliferee among others stand 
out as orders the members of which do not readily bleach, while 
members of the Caryophylleze, Cruciferee, Leguminosz, and 
Liliaceze are commonly readily bleached in alcohol alone. 
II. Methods. 
A. BLEACHING IN go PER CENT. ALCOHOL. 
Reference has already been made to the bleaching action of 
alcohol (page 219). 
The essential points to be observed to secure success may bear 
repetition. They are :— 
1. The immediate immersion of the material in the 
alcohol as soon as gathered. 
