44 8 Spalding.— On the Traumatropic 
and Firtsch 1 , and recent critical studies of Czapek 2 prove 
beyond question the sensitiveness of the root-tip to gravitation 
and the existence of induction resulting in geotropic curvature. 
Thus the evidence obtained from various independent studies 
of the root and other organs, indicates that traumatropism 
falls into a general class of phenomena which includes those 
of heliotropism, geotropism, and other growth-curvatures, and 
that the same principles are to be applied in its study. 
The phenomena of regeneration, to which reference has 
been made in the record of experimental work, affords 
additional and important evidence bearing upon the question 
in hand. It has been seen that roots wounded at the tip, 
provided the injury does not extend beyond the punctum 
vegetationis, rapidly become regenerated, and in the course 
of some three days, more or less, the tissue that had been 
destroyed is replaced by new, the restoration finally, in many 
cases, being so complete as to leave little, if any, trace of the 
wound. Such a process is necessarily, and in the strictest 
sense, physiological. A new and different set of conditions 
has been introduced, and to these, as to a specific stimulus, 
the cells of the punctum vegetationis respond in a specific 
manner 3 . In this response the energies of adjacent cells 
must necessarily be taxed to meet the demands of a condition 
that did not exist before the injury. Thus it is certain that 
in regeneration the growing-point responds to the very 
injuries that traumatropic curvature follows and from which it 
results. The phenomena go hand in hand, and it seems 
impossible not to regard them as two different forms of 
Nachwirkung resulting from the same cause. 
The biological significance of traumatropism is also most 
clearly seen when considered in connexion with regeneration. 
In case of injury to the growing-point of the root it is 
essential to the welfare of the plant that repair should take 
1 Ber. d. bot. Gesellsch. II, 1884, p. 248. 
2 Unpublished investigations conducted in the Botanisches Institut of the 
University of Leipzig : see Annals of Botany, this vol., p. 317. 
3 Pfeffer, Pflanzenphysiologie, II, p. 172 et seq. 
