494 Effect produced on certain Plants by Frost. 



sun-rise a thermometer suspended from a north wall, under 

 the protection of a coping, was observed to stand at 29°; 

 the dew point at six in the morning was 32°, with a temper- 

 ature of 40°. The real degree of cold during the night was, 

 however, considerably greater than was indicated by the 

 thermometer upon a north wall. Tn an instrument used for 

 ascertaining the degree of cold to which a body is exposed, 

 so isolated, as to be as far as possible out of the influence of 

 radiation from surrounding objects, the mercurial column 

 was depressed to 19°, an intenseness of cold which, as will be 

 hereafter seen, some of the hardiest of our forest trees are 

 incapable of enduring when in a state of vegetation. 



The following is a List of the various Plants which were 

 injured by the Frost. 

 Trees and Shrubs. 

 » Azalea viscosa 



versicolor. 



nudiflora. 



glauca. 



Robinia Pseud-acacia ; all the varieties. 

 hispida. 



Fraxinus ; all the species except parviflora and 



horizontalis, and especially 

 Fraxinus nana. 



Theophrasti. 



excelsior. 



— excelsior verrucosa. 



Cercis Siliquastrum. 

 Ailanthus glandulosa. 



