-•'"•»' V 



^iLIBRARY 



PERMANENT WILTING IN PLANTS 



thus derived, for the three soils here employed, respectively, 

 are appended also to table I. 



The containers used for the plants were tinned sheet-iron 

 cylinders, each with a capacity of either 500 cc. or 2000 cc, 

 according to the plants employed. These were perforated at the 

 bottom to allow for drainage. 



Zea mays Lin., a quick-growing variety, Phaseolus vulgaris 

 Lin., and Capsicum annuum Lin., a variety of Spanish pepper 

 much cultivated in southern Arizona, were used. The seeds 

 were planted directly into the cylinders and the "cultures thus 

 prepared were kept in a lath shelter with walls and top so con- 

 structed as to allow about one-half of the total sunlight to pass. 

 Here the plants were cared for and allowed to grow to such an 

 age and stage of development as to assure apparently reliable 

 results. 



From twelve to twenty-four hours before the plants were to 

 be used, they were watered and dripping was allowed to cease. 

 The upper surface of the soil and also the perforations at the 

 bottoms of the cylinders were then sealed with plastiline (the 

 same as was used by Caldwell), to prevent evaporation from the 

 surface of the soil. Since a very long time was apt to elapse 

 (during which the plants might alter considerably (see Brown, 

 loc. cit., page 132) before the advent of permanent wilting in 

 the case of those cultures which were placed in the glass box, 

 it was found expedient to water these but sparingly or not at 

 all before sealing. Thus it sometimes happened that permanent 

 wilting occurred in the glass box earlier than in some of the other 

 exposures, although the latter were always characterized by 

 more intense evaporating powers of the air. 



Soil samples were taken from top to bottom of the cylinder^, 

 with a cork borer 18 mm. in diameter, in the manner already 

 employed by Brown and by Caldwell. The upper portion of 

 the soil column thus obtained, 2 cm. in length, was discarded, 

 since few or no roots occurred in this region of the soil mass. 

 This method was adopted in preference to that of weighing the 

 total soil content of the cylinders, since by repeated tests it 

 yielded results quite in accord with those of the latter method 



