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SECTION IV. 
CONCLUDING REMARKS ON THE VEGETABLES REPRESENTED IN THE PLATES, 
AND ON FOSSIL VEGETABLES IN GENERAL, TOGETHER WITH AN AC- 
COUNT OF THE MANNER IN WHICH SLICES ARE OBTAINED FOR MICRO- 
SCOPIC EXAMINATION. 
Tue first general remark which I have to offer respecting the fossil vege- 
tables figured in the Plates, is, that their concentric layers present the same 
irregularity as those of our recent plants. It will be seen from Figs. 1, 2, 
and 6, of Plate V., and from Fig. 1. of the lower part of Plate IV. in par- 
ticular, that some of these layers are much broader than others in the same 
species. An inference to be made from this circumstance is, that the cli- 
mate which existed at the epochs when these vegetables grew, resembled ours 
in the irregularity of its successive summers. If, at the present day, a warm 
and moist summer produces a broader annual layer of wood, than a cold or 
dry one, and if fossil plants exhibit such appearances as we refer in recent 
plants to a diversity of summers, then it is reasonable to suppose that a simi- 
lar diversity formerly prevailed. 
The Coniferz of the coal-formation and mountain limestone group, have 
few and slight appearances of the lines by which the annual layers are sepa- 
rated. The trees of our present tropical regions have also few and slight 
appearances of these lines. Therefore, at the epochs of these formations, 
the changes of season were probably as little marked as they are in our tro- 
pical regions. 
Again, the condensation observed towards the outer margin of each 
woody layer of the trees of our cold and temperate climates, and which is 
attributed to the increasing cold of the latter part of the autumnal season, is 
F 
