450 Spalding . — On the Traumatropic 
adaptation to the environment, in either case it is strictly in 
accordance with all we know of the habits of plants that 
the root should now be in possession of the power of turning 
in self-protection from an enemy it could not overcome, 
repairing whatever injuries have been inflicted, and then 
resuming its normal growth and functions. 
Two questions of much theoretical interest present them- 
selves in connexion with the one chiefly studied and thus far 
under discussion. The first, in regard to the mechanism of 
the movement exhibited in growth-curvatures of the root and 
other organs, has engaged the attention of physiologists for 
many years, and as yet is not satisfactorily explained. The 
present study throws no direct light upon it, but suggests the 
necessity in its further study of taking into account the various 
changes that take place while Nachwirkung is delayed by 
mechanical means. The second, regarding what is known as 
the latent period, i. e. the period intervening between stimulus 
and visible after-effect, has received such attention as could 
be given it, and our knowledge is thereby increased to the 
extent of the data accumulated in the various experiments 
with roots confined in casts. That the latent period may by 
such artificial means be extended for more than a week is 
a fact of sufficient physiological importance to warrant the 
more extended investigation which it is hoped may hereafter 
be given to it. 
