i8 WONDERS OF PLANT LIFE 



renewal of activity is simply due to the fact that 

 the cold weather is gone ; but this does not offer 

 a complete solution of the problem. 



In the autumn the conditions are often mild 

 for weeks together, yet the trees do not start 

 into leaf. It may be suggested that it is the 

 increase in the intensity and the amount of sun- 

 shine which arouses the plants from their winter 

 slumber. This can hardly be the case with the 

 large number of herbaceous plants with root- 

 stocks inches below the surface of the soil, yet 

 these respond to the call of spring no less readily 

 than the deciduous trees and shrubs. Even 

 more difficult to explain is the behaviour of the 

 aquatic species, such as the Water Lilies. The 

 roots of these plants are buried in mud many feet 

 deep under water how can they possibly be 

 aware of the arrival of the new season ? Yet 

 quite early in the spring these plants begin to 

 stir into activity. Most strange of all in con- 

 nection with the problem of the plant and the 

 seasons is the story of the Soldanellas, a small 

 species which exists on the lower slopes of the Alps. 

 When the flower stems are in their most active 

 state of growth they release a considerable amount 

 of heat. In this way they will bore a course up 

 through a thick coating of ice and snow to the 



