5^ THE PLANT WORLD. 



was replenished daily, but the flow of water was discontinuous. 

 The result was, of course, a closer simulation of the actual occur- 

 rences at the time of the rainy season. 



The first run of water was applied 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 Ijan- 

 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. ( )n July 9. the largest leaves were 2 centimeters long, 

 and the branch in question, together with its neighbors were 

 photographed (Fig. 8). In looking at this picture one nuist 

 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 II, at 5 P. M., we had the first shower of the rainy 

 season, the amount of precipitation being one and one-tenth inches 

 within two hours, drenching, of course, all the vegetation. On 

 the following day (the twelfth) at four P. M., it was quite evident 

 to the eye that the buds had made a start. By July 13, the slender 

 conical buds along the whole extent of the stems were 7 to 8 milli- 

 meters long. On July 14 at five A.M., the rosettes of leaves were 

 well formed; the length of the largest leaves was 1.5 centimeters, 

 their size being, however, quite uniform. On July 15, the photo- 

 graph forming figure 9 was taken. It will be noted that the leaves 

 on the irrigated stem were at that time much larger than the 

 freshly formed leaves, that is, those produced after the rain, and 

 as a result of the stimulus thereby given. 



It will be noted that the development after the rain was more 

 rapid than after irrigation, notwithstanding that the water was 

 applied artificially from time to time during the period of growth 

 under observation, while the wetting by rain occurred but once. 

 The fact, however, must not be lost sight of, that following the 

 rain there is a marked rise in the relative humidity, though I re- 

 gret that I did not take observations on this point at the position 

 of the plant. Then, too, the ground got a good soaking, and it 

 is remarkable how rapidly the soil becomes moist for a consider- 



