CERTAIN DICOTYLEDONOUS AND CONIFEROUS LEAVES. 243 
laminated carbonaceous clays and loams and thin impure pipe-clays arranged 
for the most part in overlapping lenses of all sizes up to a few hundred yards 
in diameter. He states that ‘Physically the fresh-water beds of the 
Bournemouth Series conform to the delta type of deposit." Gardner con- 
sidered that the river which deposited these beds flowed from the west in a 
south-easterly direction somewhat parallel to the inland direction of the 
chines, depositing its sediments at the very base of the Middle Eocene 
formations. Clement Reid pointed out how greatly the plants vary in the 
different lenticular masses of clay in which they occur so that they appear to 
have been deposited in very small basins formed by backwaters of the river, 
which was apparently constantly changing its channels. 
Isolation and Clearing of the Cuticles. 
The leaf material was cleared either in concentrated nitric acid and 
chlorate of potash, or when this treatment was found too drastic, in Eau de 
Javelle, which acts more slowly, and was then washed with 20 per cent 
ammonia, For full details of methods of treatment see Nathorst (1908), 
Bather (1908), and Thomas (1912). For mounting these preparations of 
cuticle, water stains followed by glycerine and glycerine jelly were always 
found more successful than spirit stains followed by absolute alcohol, clove 
oil, and balsam. Attempts to differentiate cells by staining were not 
extremely successful. The guard cells of the stomata stained a little more 
deeply than the ordinary epidermal parenchyma, but all chemical differences 
in the various types of epidermal structures evidently became obliterated on 
fossilization. Methyl green, methylene blue, and saffranin were found to give 
the best results in sharply delimiting the cells. For comparison with the 
fossil leaves, very numerous preparations of recent leaves were made, and 
the procedure followed was exactly the same in the two cases, so that any 
post-mortem changes would be similar and comparable. Among the various 
leaves selected for examination, some of the genera described in Gardner’s 
paper were dealt with first, in the hope that the anatomical structure of the 
cuticles would confirm the accuracy of the identifications which were based 
on the external characters of these leaf-forms. The diameters of the cells in 
the various leaves were measured by means of Hutchinson’s Co-ordinate 
Micrometer and a stage micrometer. It was found that within the limits of 
the writer’s observation, different species of a single genus showed very 
similar cuticular form: thus certain genera, e.g., Salix, Quercus, Fagus, 
could be readily identified. 
There is not yet a definite consensus of opinion as to what we are to 
consider really critical characters in epidermal tissues. Thus, for example, 
in fossil Cycadophyta sinuation of the wall is shown to be a diagnostic 
character of ordinal rank (Thomas and Bancroft), whereas Dr. Marie Stopes 
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