62 BULLETIN 545, U. S. DEPARTMENT OF AGRICULTURE. 



held together by the intertwining of the roots was wrapped in burlap 

 for purposes of transfer and immediately placed upon suitably cut 

 wire screen (see Plate I), which, when fitted and fastened together 

 around the soil body in the form of a basket, was placed in the hole 

 created by the digging of the plant. In this manner the plant was 

 not subjected to too rapid drying and its normal functions were 

 unimpaired. After the plant had fully recovered from any slight 

 disturbance due to digging, it was elevated slightly in order to 

 increase the rapidity of the drying process. The wire-basket method 

 made the plant portable, a very desirable feature in field work since 

 the plant could easily be removed from the field during showers and 

 when in a wilted condition prior to soil sampling and placed under 

 shelter — in this case in a carefully-placed 14-ounce canvas tent — and 

 thus protected from direct effects of wind and sun when the specimen 

 might recover its turgor if not wilted excessively. 



The other method of ascertaining the water requirements was to 

 dig away the soil on all sides of the plant, leaving in place the central 

 core of soil supporting the roots, the size of which would depend upon 

 the spreading habit of the root system (see Plate I, fig. 2). This 

 method was used especially for certain species with deeply pene- 

 trating taproots, such as wild celery (Ligusticum oreganum) and wild 

 buckwheat (Polygonum pliytolaccaefolium). These, it was found, 

 would not respond normally to the wire-basket method of treatment. 

 The drying process brought about in this way, owing to the fact that 

 the water supply was not wholly cut off from below, was slightly more 

 gradual than in the case of the wire-basket method, but the results 

 of the tests for species which did not have a distinct taproot, such as 

 grasses, proved to be virtually the same as those secured for the same 

 species by the wire-basket method. When the plant reached a con- 

 dition of pronounced wilting and turgor could not be recovered, two 

 representative soil samples were taken, weighed immediately to avoid 

 possible discrepancy due to evaporation, placed in a soil-drying oven 

 and subjected to a temperature not exceeding 212° F. for several 

 hours until they were dry, then reweighed. The difference between 

 the dry weight of the samples and the weight when taken at the time 

 the plant was in a wilted condition represents the amount of moisture 

 remaining in the soil at a time when the root hairs were unable, under 

 the conditions, to absorb moisture rapidly enough to maintain the 

 form of the plant and finally to recover its turgidity. The depth and 

 location at which soil samples were taken were regulated by the 

 depth of penetration and position of the roots. This operation was 

 followed by protecting the specimen from the direct effect of sun and 

 wind by placing a small tent shelter over it. In all cases the soil 

 moisture figures given are based upon specimens which failed to 

 recover their turgor, unless otherwise stated. All moisture require- 



