268 BOTANICAL GAZETTE [APRIL 
tion of the current, and many counted as neutral deviated from : 
a straight course. That this very irregular direction of growth 
in streams of low speed is due to the movement of water is 
made known from the fact that these seedlings produce very 
straight roots in still water. In a control test, fifteen seedlings 
suspended with their roots in still water grew straight. It seems 
to be demonstrated, therefore, that currents of water with a 
velocity less than 2 per minute are not able to call forth a 
positive response in the primary root of Brassica alba. 
The results obtained in attempting to determine the mini- 
mum, optimum, and maximum velocities for inducing a theo- 
tropic response in Raphanus sativus show that this plant agrees 
very closely in these respects with Brassica alba. Since these 
results can be most briefly given in tabular form, we ides 25 
resort to that method of presentation. 
TABLE V. 
EXPERIMENTS WITH RAPHANUS SATIVUS, showing relation of response to velocity. 
Period, 8 to 24 hours, the record being made when the most curves — . 
each experiment. 
ae 
Total seedlings | Temp in air | Flow per mi Percentage of curvatures oe 
22 to 24° 25to 100" | 72 €=+ H ene 3 gz 
117 22 to 24 50 to 500 03. - =f. - 
24 23 600 to 100 [12.5 =+ &F. 5 208 = 
To 22 to 23 1000 to 2000 o =+ ae a 
2 : . ag ve fout of : 
From this table it appears that ponte one : 
the roots remain neutral in a velocity between 25 ey 
E per minute, that the optimum speed lies between 5o™ will ale 
_ per minute, and that velocities above 1000™ per minute . 
call forth a positive response. This table, — 
: or two units a ne more accurate meee were ma 
_ Not hes is the largest number of positive ana ; 
