1902] THE RHEOTROPISM OF ROOTS 271 
This is the only plant that has not always given a negative bend 
ina velocity of 2000™ per minute. 
An examination of my notes on all experiments shows that, 
without having determined the optimum velocity precisely for 
any species, all of the plants I have worked with give the most 
constantly positive responses and attain the greatest angles in 
velocities between 100 and 500™ per minute. 
Il. LATENT PERIOD AND AFTER-EFFECT. 
A remarkable fact in the rheotropic response of roots is the 
extraordinarily long latent period. It is true that Berg; states 
that he obtained curves often within thirty minutes. But he 
gues neither the precise plants, nor temperature, nor velocity 
wah Which this result was obtained. When he used the reading 
microscope in an experiment with Zea mays, he found a minimum 
latent period of one hour. Juel (2. ¢., p. 529), with Vicia sativa, 
temperature and velocity not given, believed he could detect 
initial curves in two hours. ae 
My own results agree with those of Berg and Juel, but they — 
_ have been extended over a larger number of plants, and have | 
gat in also the relation of velocity of current to time of 
_ Response. The following tables will show how these plants have © 
: - Observations were made at the intervals recorded in 
3 and hence the curvatures recorded for any hour, — 
— ‘irst, may have begun between the time recorded and — 
tgs observation. Close attention failed to reveal any — 
with a... than eighty minutes. Observation was made — 
ae ceed eye, and we may assume, therefore, that the — 
7 cope would have shown a shorter latent period © 
= 8a 
ete minutes. Reference to fig. 0, page 275, will convince 
* Several of those curves must have begun at least ten to 
OER : ie earlier than the time recorded. ee 
= . “fin the following table indicates that no 
Was made at that time. (oe 
— : iiber Rhetropismus. Lunds Universit. Arsskr. 357: no. 6. 1899- 
