fig FORESTRY OF NORWAY. 



the summer, and the average greatest heat of the summer, 

 are not the same thing ; the average cold of winter, and 

 the average greatest cold of winter, may be very different ; 

 and the greatest degree of heat, or the greatest degree 

 of cold, is not indicated by either the average greatest 

 heat or the aveiage greatest cold. A very much higher 

 temperature than the average may be necessary to the 

 maturing of fruit or seed, and the occasional occurrence of 

 of a degree of cold, considerably in excess of the average 

 degree of cold, may prove fatal to plants which could 

 have withstood even a lower average cold, without 

 detriment. 



It may be accepted as a general statement that heat 

 promotes vegetation, and that cold itself, a negative thing, 

 operates negatively in checking it, inasmuch as it is an 

 absence of the heat requisite for vigorous vegetation; 

 but greater cold, amounting to frost, may prove positively 

 destructive by freezing the sap, which in its expansion 

 bursts the sap vessels, as the expansion of water freezing 

 in pipes bursts these pipes. A heat in excess of the range 

 of temperature within which a tree flourishes may limit 

 its reproduction by seed by causing it to go all to wood ; 

 and a degree of cold in excess of that range may limit its 

 capabilities of bringing its seed to maturity, producing, 

 it may be, only a stunted growth ; while an excess of 

 cold beyond what would be followed by such a result may, 

 as has been stated, kill the tree by the rupture of sap 

 vessels through the expansion of the sap in freezing. 



Dr Broch has collected details of observations of the 

 temperature of Norway in respect of all of these particulars. 

 He states that it is only of late years that observations 

 such as are desired have been made. There exist for 

 certain places a complete, long-continued series of obser- 

 vations. But these stations were limited in number; 

 and though sufficient for the localities at which they were 

 made, and as such valuable, the geographical distribution 

 of these stations was not the one most favourable for 



