THE RHEOTROPISM OF ROOTS 343 
_ That the relatively small number of positive responses in the 
foregoing tests with Brassica alba does not necessarily indicate a 
lack of sensitiveness in the root-tip is shown by results following 
the application of the water-jet to the elongating zone, this part 
faving been proved sensitive by Juel’s work as well as my own. 
In one experiment with the highly sensitive Brassica alba, the 
water-jet met the root 2 to 5™™ above the tip, yet after a period 
‘twelve hours, of the six roots only two were positive, while 
one Was negative and three were neutral. However, in a total 
of four experiments of this nature with Brassica alba, the seven- 
teen roots showed twelve positive, two negative, and three neu- 
tral. This is certainly less equivocal than the results obtained 
from the same species when the water-jet was applied to the apex. 
: In conclusion it may be said that the experiments with the 
‘Nater-jets have indicated a rheotropic sensitiveness for the apical 
millimeter of the root. ee 
: 
2. Experiments with cylinders of paper and of collodion. — 
: Another Series of experiments to locate the sensitive area | Pe 
a ‘ted with cylinders of paper and others of collodion, in 
ch were cut apertures to admit the stream- eee 
‘Mater. Fig. rg shows the form of these 
& The paper cylinders were made of 
Paper held in form by paraffin, and the 
. 
tt by in 25 ae being subsequently dissolved 
‘tods a in water. To prepare these 
“™mercial cane sugar was dissolved by 
7 ud Tolled into small rods between the 
