208 ; [Guayule. 



Experiment 1390. Two seedlings of nearly equal size were planted 

 January 24, 1908, in a 5 -gallon oil-can, half of which contained 

 a soil made up of coarse gravel and fine soil (of the latter only 

 so much as would go between the gravel) , while the other half 

 contained uniform, finely-sifted soil of the same kind. The 

 watering was equal for both sides, and sufficient to keep an 

 abundance of water available. The subsequent growth in the 

 plant in gravelly soil was very much more marked, as shown in 

 the left-hand plant on plates 18 to 20, the limit of growth for 

 the year being nearly reached in four months. This plant, which 

 weighed 8 ounces, produced fully 2,000 seeds. The development 

 of roots was correspondingly greater in the gravelly soil, and 

 careful removal of the roots showed that they were confined 

 chiefly to this soil, though occasional roots of each plant reached 

 over into the territory of the other. However, it should be noted 

 that there appeared to be a tendency of the roots in gravelly soil 

 to grow toward the fine soil, as seen in plate 20, fig. A, in which 

 the plants are oriented with respect to each other as they grew. 

 In these experiments, therefore, the gravelly soil was more favor- 

 able to root-development, a result which appears to harmonize 

 with agricultural practice. 



IRRIGATION. 



If large numbers of seedlings are to be raised, the method of watering 

 will introduce a material element of expense, aside from the cost of the 

 water. Hand-watering of the surface would prove to be laborious and 

 expensive. For this reason a method of subirrigation was tried, with the 

 results as stated above. Additional evidence is as follows: 



Experiment 141. To test the relative value of subirrigation, with 

 and without shade, as compared with surface watering. Four 

 trays with i-inch paper tubes (plate 45, fig. A) were filled with 

 limestone soil mixed with gravel, each sown with i ounce of seed. 

 (I) Placed on the surface of the ground and shaded by a thin 



white muslin screen. 

 (II) The same, but without shade. 



(III) Placed in a melga, and shaded as above. 



(IV) The same as III, without shade. 



Ill and IV were watered by subirrigation ; I and II by surface water- 

 ing, and served as a check on III and IV. It was noted that it 

 was very difficult to keep II wet enough. The surface of IV 

 was never dry. 



In both shaded trays the germination was far in excess of that in the 

 control. In both the subirrigated trays taken together, the germination 

 was over twice that in the surface-watered trays, though it was slightly 

 more in the shaded, surface-watered tray than in the unshaded, subirri- 

 gated tray. The result indicates clearly that subirrigation with shade is 

 the most favorable of the four conditions. It should be noted that tray III 

 was left unshaded after February 13, in order to avoid extreme etiolation, 

 and this may have lowered the subsequent rate of germination without 

 vitiating the general result. 



