IN USE AT THE ROYAL BOTANIC GARDEN. 237 
injured, this particularly so in dealing with material already 
preserved. 2. The operation takes considerable time. 3. Speci- 
mens are liable to be cut through by the thread if they are at all 
heavy. 4. The thread tying the specimen is visible often, and 
detracts from the appearance of the preparation. 
II. Methods. : 
I. CEMENTS FOR ATTACHING SPECIMENS TO 
MOUNTING GLASS. 
A, CEMENTS USED WITH ALCOHOL. 
1. For light objects. 
Photoxylin is the cement invariably used with spirit material 
for light and small objects. 
As obtained from Grubler of Leipzig it is a clear, slightly viscid 
fluid, and is ready without further preparation for use. The 
advantages attaching to its use are several. Specimens are 
quickly fastened to the support, and the operation involves little 
risk of injury to the preparation. Remaining transparent as the 
cement does, it is practically invisible. Its disadvantages are two. 
It can only be employed when the preservative used is strong 
alcohol, and it will not support heavy preparations, 
The specimen to be mounted is taken from the alcohol in 
which it has been hardened and dehydrated, and the excess of sur- 
face alcohol is removed with filter paper or blotting paper. Itisthen 
placed in position on the glass or mica mount and a small quantity 
of photoxylin by means of a pipette is dropped upon it at the 
points at which it is to be fixed. The glass sheet with the speci- 
men attached is then carefully laid in an open trough of 80 per 
cent. alcohol present in sufficient quantity to cover the specimen. _ 
It is left in this for about a minute. The photoxylin sets as a 
firm transparent jelly, and the mounting glass with the specimen 
fastened to it is now transferred to a vessel containing 90 per 
cent. alcohol. From this it may be moved to the exhibition jar 
containing go per cent. alcohol, 
After the photoxylin has been applied it must be left to set in 
the air for a time, varying from a few seconds to as much as a 
minute, until in fact a slight film forms over its surface. If 
immersed in alcohol too soon the photoxylin is washed off and it 
