Plant Impressions or Incrustations . 387 
employed with the above-mentioned leaves of Eretmophyllum and Thinn- 
fcldia. This type of preservation may generally be detected by examina¬ 
tion of the fossil on the rock. Such a fossil shows, particularly when wet, 
a characteristic brownish coloration due to reflection from the surface of the 
rock through the semi-transparent plant substance. It is possible that this 
type of fossil was produced by the decay and dissolution of the mesophyll 
4 a 
Text-fig. Cladotheca undans (Halle) : i, transverse section of sorus embedded in the rock; 
2 , ditto, upper surface of lamina exposed; 2 a, surface view of 2 ; 3 , transverse section of sorus 
with portion of lamina removed, exposing some of the underlying sporangia ; 3 a, surface view of 3 , 
showing a row of sporangia on each side of the vein ; 4 , transverse section of sorus in a transfer 
preparation ; 4 a , surface view of 4 , showing the sporangia covering the underlying vein. The matrix 
is represented by dots and the coaly material of the fossil by vertical lines. In 4 the balsam is repre¬ 
sented bv short vertical stiokes. 
J 
or softer tissues prior to the plant becoming buried in sediment under con¬ 
ditions in which further dissolution was inhibited. In the larger number of 
fossil leaves the mesophyll is represented by a black coaly substance which 
has to be removed before any structure can be seen in the cuticles between 
which it lies. In Schulze’s method 1 of isolating cuticles the black matter 
is removed in solution by certain reagents. 
1 Schulze, loc. cit. 
