Snow .— The Conduction of Geotropic Excitation in Roots. 45 
2. Five roots were decapitated, the tips killed by boiling, and stuck on 
again with gelatine. Roots laid horizontal. After twenty-four hours none 
had curved. Replacement of a dead tip has no effect. 
(b) Tips replaced with Gelatine. 
3. In all 76 roots were decapitated at 2 mm. from the vegetative apex, 
and the tips stuck on again with gelatine. They were then placed hori¬ 
zontal. After fifteen to twenty-four hours, 45 curved downwards, 31 
remained straight. 
4. In certain earlier experiments, 13 roots were decapitated at 2 mm. 
Fig. 
1. 
from the end of the root cap, and the tips replaced with gelatine. They 
were placed horizontal. After fifteen to twenty-four hours, 9 curved down, 
4 remained straight. 
The extent of curvature in Experiments 3 and 4 varied from a slight 
curve to one of 90°. Curves of about 30° were the commonest. Intact roots 
laid horizontal for comparison were often found not to curve through more 
than 45 0 . 
Those roots which failed to curve often showed an enlargement at the 
end of the stump : this enlargement is also shown by decapitated roots 
without the tips replaced. But those that curved down usually did not 
show this enlargement, or showed it to a less extent. This suggests that in 
them the gelatine had made proper connexion between stump and tip, but 
that in those which failed to curve it had not made such connexion. 
To show the extent of curvature obtained, a favourable experiment is 
illustrated (Fig. 1). This represents a complete set of roots, operated on at 
one time. The four roots on the left were simply decapitated, and have 
been slightly displaced downwards from the base, but have scarcely curved 
