The Sensory Zone of Roots. 
BY 
FREDERICK C. NEWCOMBE, 
University of Michigan. 
With a Figure in the Text. 
I. Introduction. 
I N a recent paper 1 , evidence was offered to show that the 
stimulus giving the response known as rheotropism is 
perceived by the apical millimetre of Zea Mays , L., "and of 
Raphanns sativus , L. There was evidence to show also that, 
in the root of the latter plant, the stimulus was perceived 
throughout the elongating zone, and still more posteriorly, 
to a distance even 15 mm. back of the apex, this being at 
least 10 mm. beyond the limit of the elongating zone. 
This discovery was of such interest that it seemed advisable 
to extend the research to other plants, to ascertain whether 
the phenomena, observed in Raphanus , might be found to be 
general. The results obtained in such an investigation are 
reported in the present paper. 
By way of retrospect', it may be said that the various 
tropisms of roots so far determined have their sensory seat 
either in the apex or in the elongating zone. Confined to the 
apex in front of the elongating zone is the sensory tissue 
controlling the responses known as geotropism 2 , and trauma- 
1 Newcombe, The Rheotropism of Roots. Bot. Gazette, xxxiii, 1902, p. 177. 
2 Czapek, Jahrb. f. wiss. Botanik, xxvii, p. 255 ; xxxv, p. 31 7. 
[Annals of Botany, Vol. XVI. No. LXIII. September, 1902.] 
