THE BEHAVIOUR OF NORWAY SPRUCE 145 



processes presuppose a low osmotic pressure in the tissues. The high water 

 content produces high transpiration rates even in the older shoots. 



A third part of the explanation is the fact that the needles of older shoots, 

 even those of the previous year are shed during a drought, whereas the 

 needles of the ripened parts of the new shoot survive. The corresponding 

 bark gives rise to a new bud formation. 



Concurrently with the drought damage a depression in diameter growth 

 in spruce took place. A comparison between late- and early-flushing 

 individuals is very difficult because many late-flushing spruces -even trees 

 under 20 years of age-flowered and fructified in 1956 and therefore 

 suffered from an extraordinary loss of dry matter. I hope later to have an 

 opportmiity to elucidate these questions. In passing it can be mentioned 

 that drought damage of the summer of 1947 affected the early-flushing 

 spruces more than the late-flushing types (Oksbjerg, 1956, 1958). 



One of the reasons for growth depressions, during and after drought 

 periods, may be that drought can produce a colour change from dark to 

 light green or to yellow occurring in connection with a decline in the 

 N-content of the needles, decreasing from about i • 1 5 to o- 8 % of dry weight. 



Two years after the drought, in the summer of 1957, attempts were 

 made to measure the needle temperatures under different conditions, 

 though periods of drought did not occur in this summer. 



OBSERVATIONS ON NEEDLE TEMPERATURES 



The apparatus used had ten thermocouples in the simple form of bare wire 

 ends and one couple in contact with the reference temperature, an ice 

 inixture in a thermos flask. The existing couples could be sharpened 

 sufficiently, or new couples of thimier copper and constantan wires could 

 be made, for an insertion in spruce needles. This operation was less difficult 

 in needles on soft shoots but also possible in big needles on fully ripened 

 shoots. 



When the couple points were introduced in needles the electric wires 

 were fixed to suitable twigs with clothes pegs. The readings were often 

 irregular and only repeated readings which could be reproduced were 

 recorded. The galvanometer deflections could be directly converted to 

 degrees centigrade. 



The results ought to be presented in a table with detailed information 

 about weather conditions, supposed to be important for the course of the 

 needle temperature, such as solar radiation, air temperature, precipitation 

 and evaporation levels in the hours and days previous to the moment of 



