MOORLAND PLANTS 221 



pushed out their buds vigorously, but on this side 

 only. 



We can readily understand the drying effect of 

 wind, especially at great elevations, but drying due to 

 low temperature is less familiar. Sachs long ago 

 experimented on the power of absorption of roots at 

 various temperatures. He found that in certain 

 plants (Tobacco) the leaves drooped when the tem- 

 perature fell nearly to freezing-point, although the soil 

 was damp enough. Turnips and Cabbages, which 

 are naturally hardier, as natives of cold countries, 

 endured the same temperature without visible check 

 More extended observation has shown that plants 

 cannot absorb water even from a wet soil unless a 

 minimum temperature, varying according to the 

 species, is attained. The maximum of absorption is 

 got with a warm soil, and in certain experiments the 

 soil is artificially warmed to promote absorption by 

 plants. Not only is absorption checked by cold, but 

 water already absorbed may prove superfluous and 

 even dangerous. A cold wind or a night-frost pro- 

 duces most damage when the ground has been warm 

 and absorption abundant. Some plants have a 

 mechanism expressly devised to meet this contin- 

 gency. At the tip of the leaf or leaflet are large 

 water-pores, which discharge drops of water when 

 sudden cold renders the quantity of water previously 

 absorbed excessive. Many grasses and Alchemilla 

 (Lady's Mantle) have such water-pores, and if a cold 

 night should succeed to a warm, damp day, they 

 exude big drops, which are confounded with dew by 

 thoughtless people. Dew forms only beneath a cloud- 



