Roots and Shoots (Second Paper). 615 
quite independent of any correlation. It was just because 
I thought that this was probably the case, that I purposely 
omitted from consideration the variations in growth which 
immediately followed the injury. How necessary this pre- 
caution was is shown by the researches of Townsend 1 , who 
arrived at the following conclusions 2 as the result of careful 
study : — 
‘A single irritation produced by cutting or splitting the 
shoots or roots or removing the leaf-tips of seedlings tends 
to produce a change in the rate of growth of the injured and 
of the uninjured parts. 
c If the injury is slight, signs of an acceleration in the rate 
of growth will be apparent in from six to twenty-four hours 
and will continue for from one to several days. If the injury 
is severe, the acceleration will be preceded by a period of 
retardation, depending upon the severity of the injury and 
upon the condition of the plant injured. 
‘ The growth of the stems of older plants is accelerated by 
removal of a number of the roots or leaves, but is not affected 
by a slight injury to the roots. 
‘ The roots of older plants as well as of seedlings are more 
independent than are the stems or shoots 3 . 
c The change in the rate of growth of higher plants under 
the influence of a single irritation begins gradually, reaches 
its maximum in from twelve to ninety-six hours, and gradually 
diminishes until the normal rate is resumed.’ 
The results which Hering obtained by the application of the 
method of embedding in gypsum 4 , introduced by Pfeifer, mark 
1 The Correlation of Growth under the Influence of Injuries ; Ann. Bot., xi, 
p. i8 97 - 
2 Loc. cit., p. 531. 3 ‘ Kny, loc. cit, p. 280.’ 
4 Although the method of embedding in gypsum is preferable in the present case 
to that of the removal of the organs, yet it must not be forgotten that the green 
shoot, when embedded in gypsum, is not only hindered in its growth, but is with- 
drawn from the influence of light, and is consequently unable to assimilate carbon 
dioxide. It is therefore necessary for the purpose of comparing normal plants with 
those embedded in gypsum, that all the experiments should be performed in dark- 
ness (cf. Hering, loc. cit, p. 155). But results obtained by experiments in darkness 
are not directly applicable to seedlings observed in light. 
