96 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Experimental Evidence of Root Periodicity. 
Monstera, aerial root. — About eighteen successive experiments were 
made with the roots of this plant at different seasons of the year, and in 
all evidence of daily periodicity was obtained. Each observation was con- 
tinued over prolonged periods, varying from eighteen to forty-live days. 
The records were taken with the automatic auxanometer. In Plate III., 
fig. 14, there is shown a portion of a typical record of one of those experi- 
ments which was carried on during May- June 1910. The daily periodi- 
city is here well marked, the growth curve beginning to rise regularly 
about midday, attaining a maximum during the night, thereafter falling to 
a minimum during the forenoon. A four-day wave is also seen in the 
curve presented commencing on 29th May, and attaining its maximum 
on the night lst-2nd June. Two other instances of the four-day wave 
are exemplified in Plate II., figs. 12 and 13, which represent portions of 
long records made during winter and summer conditions respectively. In 
the former, the organ was exposed to an alternation of light and darkness 
in the ratio of 9:15, while in the latter the conditions were reversed, the 
ratio being 18:6. The occurrence of the periodicity under such diverse con- 
ditions of illumination is an argument in favour of its autonomic character. 
The effect of the seasonal change in the duration of the natural period 
of illumination is seen when the relative amounts of day and night are com- 
pared. Thus in Table of Statistics, Nos. 10 and 11 (page 98), the mean rate 
in both cases is greater by night, but the relative amounts diverge widely. 
For the November experiment the night amount is about three times 
greater than that of the day, whereas, in the other case, owing to the 
longer June day, the growth amount for the day period is about two and 
half times that for the night 
Vicia Faba, hypogeal roots. — The graphs of about forty experiments 
under various conditions as to light and darkness on the roots of the 
Bean were worked out, and daily periodicity was found to occur through- 
out. Fig. 15, Plate III., represents part of a record taken during the 
month of June when the duration of light to darkness was as 3:1. In 
this case the periodicity is evidenced by a rise in the growth curve during 
the day, the maximum being attained early in the evening, followed by 
a fall during the night period, the lowest growth occurring generally in 
the forenoon. 
This is exactly the converse of what is recorded by Sachs in his Dahlia 
curve, and might be regarded as an effect, in the root, due in part to 
correlation with the growth periodicity of the stem, which, owing to 
