389 
Plant Impressions or Incrustations . 
paration of Gleichenia sp. from the Cretaceous of Greenland spores closely 
resembling the modern genus Helminthosporium were found in association 
with the frond. In another preparation a spore-form was found, which is 
figured in PI. IX, Fig. 13. It is seen to consist of a mass of septate spores 
resembling forms found in the recent fungi included in the Dematiaceae, 
such as Septosporium , Cladosporium , &c. Although there is in these 
examples no very conclusive evidence, the nature of the spores strongly 
suggests that they were developed in subaerial conditions. If this is so, then 
we must suppose that the plants were rotting on the ground, and were 
subsequently inundated and covered with, the silt. 
Some General Conclusions. 
1. It is contended that the study of the usual type of fossil plant 
% 
impression or incrustation gives insufficient data for an accurate description 
of the plant, and that it is necessary to study the other surface of the plant 
as well. A method is described by which this may be effected. 
2. That in view of the uncertainty which exists at the present day as 
to the relations between form and function in plants, it is better to avoid 
trying to reach a definite conclusion as to the ecological conditions under 
which Carboniferous plants lived by the examination of a few types only, 
and that the study of the Coal Measures stratigraphically 1 gives us at 
present more reliable information as to the nature of the habitat than 
observations based on separate types of plants found in them. 
Summary. 
1. A method of examining the 'other side ' of fossil plant impressions 
or incrustations is described. Dactylotheca plumosa is quoted as an example 
of a plant in which the characters of the under surface have escaped notice 
owing to the fact that, when the matrix is split open and a fossil plant 
exposed, all hairs or other easily detached projections are removed, and an 
inaccurate representation of the plant is given. 
2. Suggestions are given of the kind of problem which the method may 
assist to solve. Examples are quoted : 
I. Psilophyton princeps. A description is given of the spine-like emer¬ 
gences on the axis. 
II. Mariopteris , cf. muricata. Epidermal structures (glands, &c.) are 
described and figured. The form of the stomata is shown to be of the 
usual type, and the structures previously described as air-pores of the 
Marchantia type are shown to be glandular hair-bases. Figures are given. 
III. Cladotheca undans . The arrangement of the sporangia in the 
sorus is described. 
1 Kendal, P. F. (1922). 
