270 BOTANICAL GAZETTE {ame 
turned against the stream, we must name the phenomenon posi- 
tive rheotropism, even in velocities below 1™ per minute, The 
case is different with the mustard. In that plant velocities below — 
2 per minute gave only 28 per cent. of obliquely positive 
inclinations to 19 per cent. of negative, and 53 per cent. of 
neutral roots. The 
differencebetween 
the number of 
positive and nega- 
tive roots in the 
mustard is not so 
great that we may 
call the excess of - 
Fic. 8.— Four roots of Raphanus sativus after stimula- di 
tion by the water current. Roots a, 4, and ¢ have been in 9 per cent. indica- 
streams with a flow of less than 2° per minute, while d has tive of a positive 
been in a stream of 200™ per minute. 
response. Withthe 
radish, however, the roots bend only in a plane parallel with 24 
the stream, and thirty-four positive roots to three negative : 
_ and thirty-three neutral require the verdict that approximately - 
: one-half the roots of Raphanus sativus are directed by a -_ 
stream with velocities ranging from 0.4™ to 2™ per minute, oF 
even by a velocity of less than 1% per minute. oe. 
: Helianthus annuus gives mostly positive responses in velocities 
from 100™ to 600™ per minute; while in one experi 
_ Six seedlings, velocities from 600™ to 2500™ per © 
root was positive, four negative, and three neutral. F ae 
vum in three experiments, with velocities from 500% to 
and 
per minute, gave nine positive roots, sixteen negative, ats 
neutral. From this we may infer that the Ne : 
least cause mechanically negative bends. pee any 
Vicia faba gives positive curves in a stronger stream veloci 
e other plant worked with. In one experiment, with Se 
_ from 600™ to 2500™ per minute, eight roots bent P 
eight negatively, and three were neutral. In another | 
‘ment with six seedlings, two were neutral, while : 
oe ee at tese™ velocity, one at dak and t 
