ii6 m.g.stAlfelt 



Two such troughs were used for each of 5 of the experimental trees. One 

 trough was empty, and the other contained a piece of the top portion of the 

 soil. This was cut from the ground below the trough, and consisted of the 

 organic layer of raw humus and litter lying on the mineral soil. The roots 

 of the trees spread in the uppermost layer of the mineral soil, and penetrated 

 to a varying depth, generally a maximum of 0-5 m. 



Interception in the crowns of the trees and in the top portion of the soil, 

 as well as the quantity of water that penetrated the top portion of the soil 

 and reached the root zone of the trees, were calculated from the values for 

 precipitation on the open ground, in the empty trough, and in the trough 

 containing the top portion of soil. 



The gaps between the trees were usually small (a few or some tens of 

 square metres), and were infdtrated by the roots of the trees. Consequently, 

 the precipitation on these areas could be utihsed by the trees. Rain gauges 

 were also set up in the gaps; they were round and smaller than the troughs, 

 having an opening of 375 cm^. In each of 4 gaps (2, 4, 10 and 74 m^) two 

 gauges were set up. One was empty, and the bottom of the other one was 

 covered with a piece cut out of the top portion of the soil-in this case 

 consisting of moss, with the htter present in it. The gaps were surrounded 

 not only by the experimental trees, but by many other trees as well. The 

 interception in the mossy layer was calculated from the values obtained for 

 precipitation. 



Calculations were also made of the rain-shielding effect of the surround- 

 ing trees -that is, of the screening effect on the precipitation (precipitation 

 is less in the gaps than on open ground) -and of the quantity of water which 

 penetrated the top portion of the soil, and reached the mineral soil, and 

 thereby the root zone of the trees. The depth to which this water penetrated 

 was determined, among other ways, by measuring the humidity of soil 

 specimens taken at various times of the year. 



Attempts were also made to measure the water uptake through needles 

 and other overground organs. Weighing of whole plants allowed determi- 

 nation of their water deficit, as well as of the changes that took place after 

 they had been immersed in water for some hours, or had stood in rain or 

 fog. It could then be estabhshed that a not inconsiderable amount of water 

 was absorbed by the overground organs, if they had previously had a water 

 deficit. In the case of the experimental trees, the exact quantity could not, 

 however, be determined. 



The whole experimental period amounted to 4 years. The collected data 

 on precipitation were divided into two periods, namely, the months of 

 September- April and May-August. The object was to permit a comparison 



