97 
1912-13.] Studies on Periodicity in Plant Growth. 
the retardatory effect of illumination, exhibits a daily maximum in the 
early morning. 
Kny {Ann. of Botany, 1894, vol. viii. pp. 265 et seq.; 1901, xv. p. 613), 
working on different lines, by a method of amputation, is led to conclude 
that no correlation exists between root and shoot growth. 
The validity of Kny’s results has been criticised by Hering (Jahr. f. 
wiss. Bot., 1896, xxix. p. 132) on technical grounds. 
Observations on this matter are in progress, and will form Part II. 
of this research. 
This curve also shows one of the greater four-day oscillations of growth 
extending from 9tli-12th June. 
The following conclusions have been deduced from comparisons of the 
various observations made up to the present : — 
1. Roots exhibit a periodicity under ordinary conditions of environment 
which differs from that of shoots. 
2. Owing to correlation, the root periodicity is affected by changes in 
the shoot rhythm, but to what extent has yet to be determined. 
Statistics of portions of the records referred to on page 94, and figured 
in Plate II., figs. 10 and 11, in relation to the four-day waves are given in 
Table of Statistics, Nos. 12 and 13, and bear on this point of correlation. 
In both cases the relative amount of growth was the same, the ratio 
of night amount to day amount being as 1 : 0*7 ; on the other hand, the 
rate ratios were different. In the first case, the day rate of the root was 
greater than in the second. The explanation appears to be that the 
growth rate of the root is accelerated as that of the stem is retarded 
under normal conditions, the root rate increasing as that of the stem 
diminishes, owing to the retardatory effect of light. Even when the 
root is exposed to shoot conditions, this acceleratory correlative effect 
persists in spite of the direct retardatory effect of light. In the second 
case, owing to the plant shoot being in continuous darkness, and there- 
fore the retardatory effect of light being removed, the greater shoot 
rate continues, and, as a correlative effect, that of the root is to a certain 
extent altered. 
General Results. 
1. There occurs in elongating plant organs a four-day periodicity 
apparently due in part to internal causes, but affectable by 
external conditions. 
2. Roots exhibit a daily periodicity, and this is correlated with that 
of the stem. 
VOL. XXXIII. 
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