ORIENTATION OF PRIMARY TERRESTRIAL ROOTS 29 1 
employed for the experiment there is no rapid and extensive down- 
ward curvature which is later flattened. Instead the root curves 
gradually downward until a position is reached varying from 60° to 
30° from the perpendicular. When the seedlings are so mounted at 
the beginning of an experiment that the roots are directed obliquely 
downward, the geo tropic curvature is slight and in the great majority 
of cases completely flattened. The root, straight throughout except 
for the curvature of the extreme tip, then generally elongates without 
further appreciable active curvature. When roots after being taken 
from the germinating bed are directed obliquely upward a longer 
time is required for the attainment of the position in which they point 
obHquely downward than when the roots are placed horizontal. Old 
roots, especially those of Vicia faba and Lupinus alhus when placed 
at an angle of 45° above the horizontal often fail to curve below the 
horizontal before growth comes to a standstill^ and inverted roots of 
these species if longer than 3 cm. at the beginning of the experiment 
often fail even to reach the horizontal. This corresponds to the 
observations of Nemec (1901, a, S. 94 ff. and 1901, h, S. 310) but his 
statements on the subject refer to roots which were under observation 
only for a period of from thirty-six to forty-eight hours after inversion. 
In many cases, though, roots which after two days are still directed 
obliquely upward or horizontally later bend gradually downward 
until they point obliquely down. There are frequently, however, 
cases in which inverted roots do not reach the horizontal even after 
as long a period as ninety-six hours. Roots of relatively large diameter 
such as those of Vicia faba and Lupinus albus in contrast to the 
slenderer roots of Pisum sativum, Ervum lens, Vicia sativa and Phase- 
olus nanus most frequently behave in this manner. In the case of 
roots placed in air at an angle more than 45° or 50° above the hori- 
2 Sachs (1874, S. 409) reported that roots of Vicia f aha, after 3 to 4 days in air 
ceased growing entirely. By exercising all possible care, I have succeded in main- 
taining a relatively active growth for 12 to 13 days after the roots were brought 
into moist air. For example, of ten roots ranging in length from 2 to 13 centimeters 
placed horizontal in moist air and subject to a temperature of 17° to 18°, the fol- 
lowing are the mean elongations for successive periods: 1st day — 2.04 cm., 2d day — 
1.99 cm., 3d day — 1.35 cm., 4th and 5th days (forty-two hours) — 2.14 cm., 6th and 
7th days (forty-eight hours) — 2,24 cm., 8th and 9th days (fifty-three hours) — 1.26 
cm., loth and nth days (forty-eight hours) — .86 cm. One of the ten roots did not 
grow during the loth and nth day and seven others did not grow after the nth 
day. Two of the ten roots, however, grew during the 12th and 13th day, respec- 
tively 1.4 and .8 cm. during the forty-eight-hour period. 
