212 VIGNETTES FROM NATURE. 



even think about its origin or meaning in any 

 way. Indeed, until certain late investigations 

 of the tertiary floras by M. Saporta, Mr. 

 Starkie Gardiner, and others, it is doubtful 

 whether anybody had ever asked himself any 

 question upon the subject at all. But these 

 investigations have shown pretty clearly that 

 deciduous trees are quite a modern novelty 

 upon our planet, things of the last two hun- 

 dred millennia or so, entirely due to the 

 immense cooling of the earth's surface which 

 began in the early tertiary period and culmi- 

 nated in the great glacial epoch. They are a 

 special product of hard times at the Pole, like 

 the white bears, the woolly rhinoceros, the 

 mammoth, and the snow-buntings. In the 

 tropics all the trees are evergreens, or at least 

 suffer no regular periodical loss of their 

 foliage ; but in the north we have few native 

 evergreens except the pines and firs, with 

 their needle-like leaves : and the two or three 

 hardy, broad-leaved exotic evergreens culti- 

 vated in our gardens or shrubberies, such as 



