PRECIPITATION IN A SPRUCE STAND 125 



It has, in fact, been found that if the changes in the stomatal vakies are 

 followed over a long period -in the spruce, for example -a large and per- 

 sistent stomatal width is present only during the first few days after a down- 

 pour (Stalfelt, 1926, 1929, p. 324). The width and duration of opening 

 subsequently decrease, as the soil dries out. After some time, the stomata 

 are found to be open only in the morning, and still later only during an 

 hour or so directly after sunrise. Similar observations have been made by 

 Pisek and Cartellieri (193 1, 1939), Pisek and TranquiUini (195 1) and by 

 Rutter and Sands (1958). 



In the present investigation, water consumption was 167 mm more on 

 the damp sites than on the dry ones. But during the rainy periods-when 

 the soil was wet through -transpiration was about as large in both kinds of 

 trees. It was not until the rain had ceased, and the ground had started to 

 dry, that transpiration began to decrease in the trees on the dry sites, 

 whereas it remained practically unchanged in those on the damp sites. On 

 dry sites, consumption is limited by the water supply. The trees utilise the 

 water suppUed during the winter-or that stored in the soil from the winter 

 months -and they would be able to consume more if the supply were 

 greater. 



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