VI.] LENGTH AND LONGEVITY OF LEAVES. 123 



In evergreen species the conditions are in many 

 respects different from those affecting deciduous 

 species. When we have an early fall of snow in 

 autumn the trees which still retain their leaves are 

 often very much broken down. Hence, perhaps, 

 the comparative paucity of evergreens in temperate 

 regions, and the tendency of evergreens to have smooth 

 and glossy leaves, such as those of the Holly, Box, 

 and Evergreen Oak. Hairy leaves especially retain 

 the snow, on which more and more accumulates. 



Again, evergreen leaves sometimes remain on the 

 tree for several years ; for instance, in the Scotch 

 Pine three or four years, the Spruce and Silver Fir six 

 or even seven, the Yew eight, Abies pinsapo sixteen 

 or seventeen, Araucaria and others even longer. It 

 is true that during the later years they gradually 

 dry and wither; still, being so long-lived, they 

 naturally require special protection. They are, as a 

 general rule, tough, and even leathery. In many 

 species, again, as is the case with our Holly, they 

 are spinose. This serves as a protection from brows- 

 ing animals ; and in this way we can, I think, explain 

 the curious fact that, while young Hollies have spiny 

 leaves, those of older trees, which are out of the reach 

 of browsing animals, tend to become quite unarmed. 



In confirmation of this I may also adduce the 

 fact that while in the Evergreen Oak the leaves on 

 well-grown trees are entire and smooth-edged like 

 those of the Laurel, specimens which are cropped 

 and kept low form scrubby bushes with hard prickly 

 leaves.^ 



' Bunbury, Botanical Fragments, p. 320. 



