17G 



that experimental research will in the future throw light upon the 

 extent of adaptation, as evidenced by anatomical structures, to 

 which plants have attained in this matter. It was during a con- 

 versation upon such points with Dr. W. A. Cannon at the Desert 

 Botanical Laboratory that the suggestion was made by him that it 

 would be instructive to see if any light could be obtained upon 

 the influence of meteoric water upon the development of leaves 

 in Fouqiiicria splcndens, the ocotillo of the southwest. I accord- 

 ingly planned three experiments which were carried out upon a 

 perfectly leafless plant, all alike in principle, but differing in de- 

 tails. In one case, the only one I shall describe, a reservoir, con- 

 sisting of a gallon bottle, was attached to the neighboring limbs 

 of a " palo verde," and a siphon arranged to lead water to a string 

 of cheese-cloth, which in turn led the water to a bandage of the 

 same cloth tied about a stem of the ocotillo three feet from the 

 ground. The fierce winds several times played havoc with my 

 arrangements, but finally I managed to adjust the apparatus to 

 the swinging of the stems by allowing slack in the cheese- 

 cloth string. The siphon ended in a capillary tube, so that 

 the flow of water Avas small and, while it ran down the oco- 

 tillo stem at times, it did not reach the ground in any case. The 

 reservoir was replenished daily, but the flow of water was discon- 

 tinuous. The result was, of course, a closer simulation of the 

 actual occurrences at the time of the rainy season. 



The first run of water was ai^plied on the morning of the first 

 of July, and this was repeated each day. The stem was thus 

 kept more or less wet for half the time. On the evening of the 

 fourth, the leaves along 12-15 inches of the stem below the ban- 

 dage showed marked development, being i centimeter long ; and 

 by the sixth of July, at three P. M., their length was 1.5 centi- 

 meters. On July 9, the largest leaves were 2 centimeters long, 

 and the branch in question, together with its neighbors were 

 photographed (Fig. i). In looking at this picture one must 

 realize that all the stems shown were at first equally leafless. It 

 will be instructive to compare the above facts with those observed 

 after rain. 



On July I I, at 5 P. M., we hat! the fust shower of the rainy 



