WATER-STRESS BEHAVIOR OF PIMA COTTON. 9 



pleted along this line it is perhaps unwise to enter into its further 

 discussion. 



Although realizing the experimental difficulties to be encountered 

 in studying the root systems of the plants in their entirety, the 

 writer attempted to trace some of the taproots to their maximum 

 depth. 



Hunt (15, p. 311) cites Bulletin 7 of the South Carolina experi- 

 ment station (1892) as reporting that in sandy soils well-developed 

 taproots were traced to a depth of 2 to 3 feet without coming to 

 their end. Balls (3) states that "the greatest depth to which an 

 unbroken taproot has actually been followed is 2 meters and 20 

 centimeters" (7| feet). Effort was made by the writer and his 

 colleague, Mr. J. Z. Richardson, to trace taproots to their greatest 

 depth on all of the plats. Departing from the usual custom of re- 

 moving soil from around the roots by means of a trowel and a jet 

 of water, small hand picks were used. Success in reaching the 

 tip of a taproot was met with only on plat 3. From a trench exca- 

 vated 12 feet in depth near the side of the plants, a taproot was 

 removed from this plat which had attained a depth of 10 feet 

 8 inches from the surface of the ground. (PL II.) On the other 

 plats several taproots were followed to a depth of 7 or 8 feet, only 

 to lose them when their direction departed considerably from the 

 vertical. The tip of one secondary root was found on plat 1 at 

 a depth of 7 feet, but there was nothing to indicate that most of 

 the roots did not extend to a depth as great as those on plat 3. 



Contrary to expectations and to statements in the literature of the 

 subject, it was found that a great number of the secondary roots 

 grew vertically downward in the soil after having grown obliquely 

 for some distance. (PL III.) From all appearances the primary 

 roots had performed their normal functions but were assisted by 

 these deep-seated auxiliaries, which at considerable depth could not 

 be distinguished from the primary roots. Upon considering that the 

 plants were spaced only 12 inches apart and that during a part of 

 the summer the water requirement for single plants was more than 

 3 pints a day, this extensive development of a deep root system does 

 not seem surprising. 



Upon examination of the roots it was found that there was little 

 difference in the root systems of the plants from the different plats, 

 either in distribution or in the size of individual roots. Caliper 

 measurements were made of the diameters of all the roots which were 

 studied. The measurements were taken on the lateral roots by ap- 

 plying the calipers about 4 inches from their point of attachment to 

 the taproot. It was found that the mean number of lateral roots over 

 one-eighth of an inch in diameter was 2.8, 2.7, 3.0, and 2.6 per plant 

 for plats 1, 2, 3, and 4, respectively. 

 69616—22 2 



