On a New Method of investigating Fossil Plant 
Impressions or Incrustations . 1 
BY 
JOHN WALTON, M.A., 
Junior Demonstrator in Botany , Cambridge. 
With Plate IX and one Figure in the Text. 
Introductory. 
U NTIL comparatively recently in descriptions of fossil impressions, or 
incrustations as they are more correctly called, authors have generally 
confined themselves to descriptions of the external morphology of the plant 
as it is exposed on the surface of the rock. The source of information 
is thus limited to one surface of the plant. Refinements have been used in 
later years. The £ collodion film method ’ 2 suggested by Nathorst has 
enabled us to investigate with greater facility the finer details of surface 
markings. Nathorst’s method consists in taking a thin transparent cast of 
the surface features by applying a drop of a solution of collodion in ether to 
the surface of the fossil. A tough film of collodion is formed on evapora¬ 
tion of the solvent; this can be stripped off and examined by transmitted 
light. The collodion method is of great assistance, as it is very difficult to 
examine the surface of a rock under the higher powers of a microscope 
owing to the necessary use of reflected light. In some instances, however, 
use may be made of one of the improved forms of vertical illuminator. 3 
A i-in. objective can be used conveniently with this instrument. The 
preservation must be good and the surface of the plant must not be pitted 
by contact with coarse particles in the matrix in which it has been em¬ 
bedded. 
I have made use of the vertical illuminator for the examination of 
1 Examples of fossil plants prepared by this lriethod were exhibited by the writer in Section K 
(Botany), British Association, Hull, 1922 . 
2 Nathorst, A. G. (1907). For a description in English see Bather, F. A. (1907). 
3 The writer is indebted to Mr. S. M. Wadham, who suggested that the Leitz-Wetzler vertical 
illuminator might be used in the examination of fossil plants. 
[Annals of Botany, Vol. XXXVII. No. CXLVII. July, 1923.] 
