1912-13.] Studies on Periodicity in Plant Growth. 
85 
VIII. — Studies on Periodicity in Plant Growth. Part I.: A Four- 
Day Periodicity and Root Periodicity. By R. A. Robertson, 
M.A., F.L.S., and Rosalind Crosse, B.Sc., Carnegie Research 
Scholar, Botanical Department, The University, St Andrews. (With 
Three Plates.) 
(MS. received June 12, 1912. Read November 18, 1912.) 
The immediate purpose of this research has been : — 
1. To investigate whether a presumably spontaneous growth variation 
amounting to a four-day rhythm which had been observed in certain 
organs of limited growth was an individual idiosyncrasy or was of general 
occurrence in plants. 
2. To examine the growth rhythm in roots and ascertain if any cor- 
relation existed between the respective rhythms of root and shoot in the 
same plant. 
The ultimate aim is to determine by an examination of the rhythm 
phenomena in higher and lower plants whether a fundamental rhythm 
exists based essentially on periodic chemical changes taking place in the 
living matter of the cell, that is, whether processes of anabolism and 
katabolism of rhythmical recurrence find expression cumulatively in varia- 
tions of macroscopic magnitude. 
The classic researches of Sachs ( Arb . Bot. Inst., Wurzburg, 1874, Bd. 1, 
pp. 99 et seq .) and of Baranetzsky {Mem. Acad. Imp., Petersb., 1879, 7 Ser., 
vol. xxvii. pp. 1 et seq.) laid the scientific foundations of our knowledge of 
the phenomena of periodicity. 
Sachs introduced precision apparatus, and first demonstrated experiment- 
ally the spontaneous regular variation constituting the grand period of 
growth, the induced variations associated with the regular alternation of 
day and night, known as the daily periodicity, as well as spontaneous 
irregular variations dependent on causes inherent in the ceil itself. He 
further showed that the daily periodicity — the retardation and acceleration 
of growth in length associated with the regularly recurring alternation of 
day and night — was not a simple light- variation effect, but was partly a 
resultant reaction to a combination of stimuli consisting of variations of 
light-intensity, of temperature and of humidity, in so far as the latter 
influenced the turgor of the cells. 
