MAY 31 1912 
LIBRARY 
NEW YORK 
BOTANICAL 
GARDEN. 
Remarks on the Oecology of Coniferae. 
PERCY GROOM, M.A., D.Sc., F.L.S. 
Assistant Professor of Botany, Imperial College of Science and Technology , London. 
I N this paper I propose to discuss three problems concerning the 
Coniferae, namely :— 
i. The cause of their xerophytic foliage and tracheidal wood. 
2. The cause of their survival in competition with dicotylous trees. 
3. The cause of the suppression of many forms in past ages. 
As the physiology of the Coniferae is known only in regard to north- 
temperate forms, the discussion will solely concern these. 
The evergreen nature of the Gymnospermae has long been admitted 
to be primitive in the class, and in the sub-group Coniferae. The evergreen 
leaves of Coniferae display xeromorphy in their relatively and usually 
absolutely small surface, and exhibit xerophytic structure in their epidermal 
structure and often in other respects (hypoderma). Even the deciduous 
larch shows these ancestral features stamped on the form, and, to a slight 
extent, on the epidermal structure of the leaves. 
The xeromorphy and xerophytic structure of evergreen coniferous 
leaves were, for a time, regarded as providing protection against the cold of 
winter, and against injury by excessive loads of snow. 
If this explanation were regarded as adequate, we should be compelled 
to assume that Coniferae living in warm temperate or sub-tropical climes 
had migrated from cold temperate regions. 
Another explanation was offered by A. F. W. Schimper (’ 90 ), 
according to whom the evergreen nature of the Coniferae must be com¬ 
bined with a slow rate of transpiration, because during the physiologically 
dry season—the cold season in cold temperate regions—absorption of 
water is largely arrested. 
That this explanation, which accounts for the survival of Coniferae in 
north-temperate regions where there is a physiologically dry season, may 
not be a complete rationale of the origin and persistence of the coniferous 
mechanism is suggested by :— 
1. The wide range of distribution as regards climate and habit of 
Coniferae. 
[Annals of Botany, Vol. XXIV. No. XCIV. April, 1910.] 
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