562 



ZONES AND REGIONS [Pt. Ill, Sect. II 



frequently covered with gum or resin. Instead of forming protective devices 

 against transpiration in winter, the leaves are more delicate than are those 

 of the tall trees in the rain-forest ; they possess a thin cuticle, thin-walled 

 mesophyll-cells, little or no sclerenchyma, a richly developed system of air- 

 containing intercellular spaces, superficial stomata. Yet in sunny situations 

 foliage is better protected against transpiration than is foliage developed in 

 the shade, possessing a smaller surface and greater thickness, a stronger 

 development of cuticle, and a weaker formation of intercellular spaces 1 . 

 The leaves, however, are always placed perpendicular to the mean direction 

 of incidence of the strongest light, instead of avoiding it by the assumption 

 of an oblique or parallel position 2 . 



In addition to these distinctions from tropical and subtropical trees 

 a further peculiarity of all trees of cold-winter zones is their much richer 

 brandling. Whilst in the former branches of a higher order than the fifth 

 are rare, in temperate trees and shrubs twigs of the sixth and seventh orders 

 are frequent and those of the eighth not uncommon. Unbranched trees are 

 unknown in cold-winter countries. 



MAXIMUM NUMBER OF THE DEGREES OF BRANCHING IN TREES 



OF THE COLD-WINTER NORTHERN BELT 



(According to Wiesner). 



Broad -leaved Trees. 



Broad-leaved Shrubs. 



Caragana arborescens 

 Cornus sanguinea . 

 Sambucus nigra 

 Viburnum Lantana 

 Ligustrum vulgare . 

 Syringa vulgaris 



2-- 



1 Stahl, op. cit. 



2 Wiesner, I. 



