2i6 VIGNETTES FROM NATURE. 



the atmosphere in the cold and gloom of north- 

 ern winters ; and the wind would only tear 

 them off by thousands and waste the chloro- 

 phyll and starches laid up in their tissues. 

 To meet this difficulty the modern deciduous 

 oaks, ashes, and elms were developed. 

 These trees do not merely allow their leaves 

 to fall off with the wind, but they make 

 actual provision for such a contingency be- 

 forehand. Each leaf-stalk is provided with a 

 row of special empty cells, which are so con- 

 structed that as soon as the leaves begin to 

 die they rot away, and accordingly let the leaf 

 fall readily, leaving a clean, dry scar, instead 

 of waiting till some violent storm wrenches 

 them off, tearing the living tissues and 

 wasting the sap by bleeding. Moreover, 

 when autumn comes on, the living and utilis- 

 able material in each leaf is first withdrawn 

 into the bark and branches, where it is stored 

 up during the winter in order to feed the 

 young leaf-buds in the succeeding spring ; 

 and then the row of specialised division-cells 



