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 J 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 s}^stem 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 
