93 
1912-13.] Studies on Periodicity in Plant Growth. 
9th June inclusive. During the earlier part, the plant was subjected under 
natural conditions to fourteen hours illumination and ten hours darkness 
per twenty-four hours period, passing at the middle and towards the 
conclusion of the record into eighteen hours illumination and six hours 
darkness. The organ had practically ceased to grow by the time the 
experiment was finished. The maximum of the grand period was reached 
on 9th May during the daytime, preceded by the four-day waves and 
succeeded in the post-maximal phase by a series of undulations which can 
be analysed into irregular compounds of longer and shorter waves. Both 
the greater amount of growth and the greater rate of growth in this case 
were attained during the illuminated periods (Table of Statistics, No. 4). 
5. j Heptapleurum petiole (Plate II., fig. 5). Observations were com- 
menced at the earliest possible moment, that is, as soon as the organ was 
sufficiently developed from the bud to allow the necessary collar being 
affixed for attachment to the registering apparatus, and were continued 
until all growth in the organ ceased, which happened about the twenty-third 
day. The dates were 21st November to 14th December, when the natural 
ratio of light to darkness was as 9:15. The readings were accidentally 
interrupted from 2nd-4th December. 
The maximum of the grand period occurred on the eighth day of the 
experiment. During the premaximal phase, the greatest growth rate was 
by day; in the post-maximal, this was repeated except during a short 
period where there occurred a night maximum. The four-day undulations 
culminated on 24th and 28th November, and about 2nd, 3rd, and 7th 
December respectively, and were followed by a few more rapid oscillations 
of less amplitude as the growth rate slowed down to zero, when the organ 
attained its full size. 
Owing to the shorter period of illumination the night amount was 
greater than that of the day, the ratio being 1 : 0*8, although the day 
growth rate was practically greater than the night rate throughout, the 
figures being night rate to day rate as 1 : 1*4 (Table of Statistics, No. 5). 
6. The rate graph of the Crocus flower axis is given in Plate II., fig. 6. 
The rate was greater during the night period, and the actual amount of 
growth was greater during the darkness period also, owing to the greater 
length of the night (Table of Statistics, No. 6). The curve shows a trace 
of the long wave of growth in the post-maximal half, but as a whole it is 
too short to demonstrate the point clearly. 
To ascertain whether the four-day periodicity was manifested in the 
material used by Sachs under equally distributed conditions of illumination 
and darkness, that is, when during the twenty-four hour periods the plant 
