Chap. VII] COLD TEMPERATE FOREST FORMATIONS 563 



Coniferous Trees. 



Larix europaca ....... 3-4 



Abies excelsa ....... 5 



Pinus Laricio ........ 5 



Taxus baccata ....... 8 



On the contrary, the size of the leaves of woody plants varies between 

 much narrower limits than in trees of the tropical rain-forest, and remains 

 generally far below the dimensions that are usual in the latter. Leaves 

 like those of Platanus and Aesculus are not ordinary features in cold-winter 

 districts ; in tropical rain-forest they would about correspond to the average 

 size and are far exceeded by the leaves of many species. The shapes of 

 leaves of the summer-green forest are very varied ; but pinnate forms are 

 not common, yet occur in, for instance, Fraxinus, Sorbus, Robinia, Juglans, 

 Negundo. Hairs are usually weakly developed or absent, except on quite 

 young leaves, where they occur more frequently as a protection against 

 transpiration, as in Fagus. 



Plank-buttresses at the base of tree-trunks are here and there indicated 

 on wet soil, as in the pyramidal poplar ; they never attain any considerable 

 development. I know of cauliflory in no cold-winter district ; ramiflory 

 only in one shrub, Cercis canadensis. 



Whilst in comparison between summer-green trees of cold-winter districts 

 and trees of the tropical rain-forest, the distinctions strike the eye more than 

 the resemblances, yet the resemblances predominate in comparison with the 

 deciduous trees of xerophilous tropical vegetation. In such xerophilous 

 tropical trees the trunks are shorter than they are in the trees of the rain- 

 forest, are comparatively thicker, have no plank-buttresses, are covered by 

 a thick scaly bark, and provided with distinct annual rings in their wood ; 

 the branching is richer, the buds are enclosed in hard scales, the leaves are 

 smaller, cauliflory is very rare. In short, such a xerophilous tropical tree 

 possesses — apart from extreme cases already described — a climatic impress 

 similar to that of an oak or an apple-tree ; the sole difference is the xero- 

 philous structure of the leaf. The comparison thus shows that it is not the 

 conditions of temperature, but those of humidity, which have induced these 

 resemblances and distinctions that are independent of systematic affinity. 

 The bark of our trees and the scales of their buds provide protection less 

 against the cold as such, than against transpiration, at a season when a supply 

 of moisture from the soil is impossible on account of the temperature being 

 too low. 



The shrubs and young trees forming the underwood of summer-forest 

 and the herbs on the ground have the typical impress of shade-plants. In 

 the horizontal branching of young elms and beeches growing in the forest, 

 Wiesner sees the expression of an effort to obtain the completest possible 



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