60 Spalding : Mechanical adjustment of suaharo 



suaharo number i {figure /), which maybe regarded as in most re- 

 spects a typical individual. This plant {plate 3) was about 12 feet 

 high, in good condition, and the observations upon it were begun 

 earlier and continued longer than on any other, thus covering more 

 varied conditions than in any other case. The furrows marked 

 were all on the north side, the points selected for measurement 

 being about halfway from the ground to the top of the plant; 

 and consequently the curves constructed from these measurements 

 show a much greater similarity than those for which the measure- 

 ments were made at different heights and on different sides. 



The observations were begun December 10. During the cold, 

 dry weather which followed, the edges of the furrows slowly ap- 

 proached, one of them losing i| of an inch in width. On February 

 6 there was a rain of 0.54 of an inch,^ and this was followed by 

 warmer weather. After this rain, the furrows expanded rapidly 

 for nearly a month. This period was probably prolonged some- 

 what as a result of some water being poured out near the plant 

 in the latter part of February. About March 2 the furrows 

 began to grow narrower, and this continued during the warm, 

 dry weather of March and April, On May 2 and 3 there was 

 a rain of about one inch and slight expansion of two furrows fol- 

 lowed. It is not known whether this expansion continued, as the 

 observations were now brought to a close. 



Inspection of the curves shows at a glance that expansion and 

 contraction of the stem, indicated by varying distances between 

 adjacent ribs, is correlated with water-supply ; a conclusion abun- 

 dantly confirmed by observations upon other individuals, especially 

 numbers 2 and 9, which were furnished wuth water from artificial 



r 



sources. 



Number 2 was situated about eleven feet from the end of the pipe 

 that carried off the waste water from the laboratory, and the slope 

 of the ground was such that the water flowed close around its 

 base. On March 12 this was changed, a trough carrying the 

 water past the plant and emptying it on the slope below, though 

 some water still probably reached the roots of the plant through 

 leakage of the trough. 



*The statements as to amount of rain are all based on the records kept at the 

 University of Arizona, some three miles from the Desert Laboratory, and 200 feet below^ 



It. 



