OUR TREES IN WINTER. 41 



provision for these changes. This they do in several 

 ways. The herbaceous plants retire below the surface of 

 the ground, and maintain life in their roots which are 

 filled with nutriment ready for a rapid growth in spring; 

 or, they store up a similar starchy material in bulbs or in 

 tubers. These three classes of herbaceous plants are rep- 

 resented respectively by the Golden Rods, the Lilies, 

 and the Ground Nut. 



In summer too, our ponds are in many cases partly 

 filled with a floating or half submerged vegetation. In 

 winter they are bare on the surface, and the water is 

 clear often to a great depth ; all the vegetation having 

 sunk to the bottom, there to contribute to the rich 

 ooze which forms the floor of most of our ponds for 

 the protection of the thick roots, winter buds and seeds, 

 which are rapidly to fill the ponds with vegetation as the 

 next summer advances. All these plants are protected 

 from sudden changes of temperature by being below the 

 surface of the earth, and they are often farther provided 

 with a mantle of snow. 



The woody plants, however, cannot avail themselves of 

 this privilege. They cannot retire beneath the surface to 

 reappear in spring. They must find other ways to with- 

 stand the cold. They must hibernate within their own 

 coverings. 



As this present flora was slowly distributed and crept 

 from point to point as the ice receded, in the last great 

 geological change, only such trees could maintain a foot- 

 hold, as were well provided against extremes of tem- 

 perature. By the continual weeding out of weaker indi- 

 viduals, and the strengthening of stronger, we have left 

 to-day the grand result of this work of nature through 

 the countless years that these plants have been adapting 

 themselves to our particular climate. 



3* 



