1919] WEAVER &- AlOGENSEN— TRANSPIRATION 397 



the demands of the root system. Thus, while the 2-year-old 

 Engelmann spruce required containers only 6.5 inches deep by 

 3.5 inches wide (these were the smallest used), the 3-year-old 

 yellow pines were grown during the experiments in containers 5 . 5 

 inches in diameter and 14 inches deep. Such containers are very 

 desirable, since they combine lightness with appropriate shape for 

 using the minimum amount of soil. 



In September, when the trees were transplanted from the pots 

 to the galvanized iron containers, they were handled in such a 

 way as to scarcely disturb the root systems. A layer of coarse 

 gravel 0.25 inches deep was placed in the bottom of each con- 

 tainer, to the side of which, extending from the bottom to the top, 

 a heavy glass tube 5 mm. in diameter was fastened with sealing 

 wax. The soil in the flower pots, having been well watered 24 

 hours previous to transplanting, and the water allowed to drain 

 through the bottom of the pot, was of such a texture that the whole 

 contents could easily be removed by inverting the pot and jarring 

 the edge while holding the soil surface intact with a piece of cloth. 

 This core of soil, containing the root system practically undis- 

 turbed, was placed in the new container. In some cases it was 

 necessary to trim away a part of the top of the conical core, but the 

 part removed was always free from roots. Previously the sheet 

 metal container had been filled to such a depth with soil of the 

 same composition as that of the core, that the plant, when put 

 in place, would be at a proper height in relation to the top of the 

 pot. Soil samples for moisture content determinations were taken 

 at this time. Any spaces in the new containers were carefully 

 filled with soil which was properly compacted. Several plants had 

 their root systems more or less disturbed in repotting, and these 

 were discarded. Finally, the pots were sealed. 



The seals consisted of petrolatum mixed with paraffin ; the latter 

 had a melting point of about 50° C. Various mixtures were used, 

 from 80 per cent paraffin and 20 per cent petrolatum (by weight) 

 at the beginning of the experiment, when the weather was hot, to 

 25 per cent paraffin and 75 per cent petrolatum in midwinter. A 

 very satisfactory seal for winter weather consists of the latter 

 mixture poured on the surface of the soil while very hot, and then 



