434 New combe . — The Sensory Zone of Roots . 
laid against this, one by one, and secured in place by a strip of 
cloth and rubber bands. While these tubes and seedlings were 
being fastened to the bar, they were kept constantly in the 
vertical position, and hence throughout the whole preparation 
there was no chance for a geotropic stimulation. As these 
tubes were arranged on the bar, none of them came nearer 
than 3*5 to 3 cm. from the middle, and the extreme ones were 
about 9»5 cm. from the middle. The interval between two 
neighbouring tubes was about i*5 cm. As the seedlings were 
secured in the paired tubes, they were adjusted so that any 
length of apex desired was enclosed by the lower piece of the 
paired tube. Thus when the bar of wood with its load was 
suspended over a revolving basin of water, with the glass-tubes 
projecting into the water, the only part of the root exposed 
to the water-stream was the portion, usually 5 to 10 mm. in 
length, between the two pieces of the paired-tube. 
As stated elsewhere 1 , it was with great surprise that 
I observed the roots of Raphanus sativus , L., making positive 
curves within glass-tubes when the part that was stimulated 
was 10 mm. distant from the apex, especially as observation 
with the horizontal microscope had shown that the elongating 
zone, when the roots are kept in water, is confined to the first 
5 mm. of the apex. The roots of Raphanns sativus , when 
10 mm. of the apex were enclosed in the tubes, showed thirty- 
four positive curves in a total of forty-eight seedlings ; and 
when a length of 15 mm. of the apex was shielded, ten positive 
curves in a total of 23 seedlings. When, however, a length 
of 20 mm. of the apex was shielded from the water-stream, 
in a total of nineteen roots, only seven curved positively, 
while four became negative, and eight remained neutral. 
Since this record was made for Raphanus sativus (early 
long scarlet), five other tests have been made with the same 
variety, and in the same manner as before. The total result 
obtained in all the experiments with this plant may be 
presented in the form of the following table : — 
Table I. Raphanus sativus with root-tips shielded from 
1 Newcombe, Bot. Gazette, xxxiii, 1902, p. 177. 
