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Proceedings of the Royal Society of Edinburgh. [Sess. 
ing over about eight days, and made up a slow rise and a slow fall instead 
of the usual slow rise and rapid fall characteristic of the premaximal phase. 
This peculiarity is seen in the part 9th to 14th April inclusive (Plate I., tig. 1). 
The mean rate of growth for the whole period of observation worked 
out to : night rate to day rate as 1 : 0*94 ; whereas the relative amounts per 
twenty-four hours period for the same proportion of light and darkness were : 
night amount to day amount as 1 : 1*8. This was due to the longer duration 
of the illumination period, which allowed of the deficiency consequent on 
slower average growth being more than made good (Table of Statistics, 
No. 1). 
2. Bryojphyllnm Shoot (Plate I., fig. 2). — This experiment was carried 
on during the winter from 18th November to 4th December, a period of 
sixteen days, when the conditions as to illumination were almost the 
converse of those in the preceding experiment — there being per twenty-four 
hours, fifteen hours darkness to nine hours illumination. The main shoot 
under observation here developed into a flowering axis, and its growth was 
therefore limited. The occurrence of the series of long: undulations referred 
to in the post-maximal of the tulip is here very marked, and evidences that 
the maximum of the grand period had been passed before the record of 
growth was begun. The mean rate of night to day growth was 
1 : 1*2 ; the relative amount of growth was greater by night, the figures 
being 1 : 07, the result of the longer duration of the period of darkness 
(Table of Statistics, No. 2). 
3. Calla Inflorescence Axis (Plate I., fig. 3). — This experiment lasted 
from 26th March to 7th May, and hourly observations were taken by day 
during that period — forty -three days — with only occasional intermittence. 
The conditions as to illumination were similar to those of the tulip. The 
experiment represents nearly the whole course of development of the Calla 
flowering axis from its appearance above ground to the fading of the 
spathe, and therefore included the grand period. The climax of the latter 
occurred during night 2nd-3rd April, and was led up to by a series of waves 
of three to four days duration ; the post-maximal phase, on the contrary, 
included several slow long undulations similar to what occurred in the 
corresponding phase of Bryophyllum. The mean rate of growth for the 
night and day periods during the forty-three days experimentation was as 
1 : 08, i.e. greater on the average during the night period, the relative 
amounts of growth were night : day as 1 : 1*5, i.e. greater by day owing 
to the longer period of illumination (Table of Statistics, No. 3). 
4. Lygodium Climbing Leaf (Plate I., fig. 4). — The continuous observa- 
tions here extended over a period of forty-one days, from 29th April to 
