48 
Proceedings of the Koyal Society of Edinburgh. [Sess. 
the length of the growing region, and can be calculated from the following 
formula : — 
L Q. Q _ Amount of growth in x time 
Length of growing region in millimetres x time in minutes" 
As there appeared to be some doubt that the length of the growing 
region in roots and shoots was a constant factor, the growing regions for 
both organs were measured daily under all four conditions of light and 
darkness, both in winter and summer, to find whether they varied under the 
different conditions. 
It was found that they did vary, so that no constant factor could be 
used for root and shoot. The divisions had to be made for the above formula 
with factors varying with each condition and with the season of the year. 
Correlation in the Growth Rate. 
The following table, giving the mean results of several experiments, 
shows the amounts of growth per hour in millimetres of roots and shoots 
for day and night during the winter and summer seasons, under the four 
conditions of light and darkness, with the varying lengths of the growing 
regions in each (G.R.) — as well as the linear growth coefficients calculated 
from these by the formula : — 
Table I. 
Amount of Growth per Hour. 
Linear Growth Coefficients. 
Root. 
Shoot. 
Root. 
Shoot. 
Day. 
Night. 
G.R. 
Day. 
Night. G.R. 
Day. 
Night. 
Day. 
Night. 
Winter — 
Normal 
•36 
•39 
8-5 
•48 
1 
•66 
40 
•0007 
•00076 
•0002 
•00026 
Intermittent 
•27 
•51 
8-5 
•39 
•59 
! 45 
•0005 
•0010 
•00014 
•00021 
Dark . 
•42 
•7 
9-0 
I-I 
1-47 
40 
•00076 
•0013 
•00045 
•00056 
Light . 
•28 
•43 
8-0 
•56 
•83 
40 
•00058 
•00087 
•0002 
•0003 
Summer — 
Normal 
•46 
•57 
8-5 
•8 
•97 
50 
•00085 
•0011 
•00026 
•0003 
Intermittent 
•36 
•45 
8-5 
•9 
I-Ol ! 
55 
•0007 
•0008 
•00025 
•00028 
Dark . 
•42 
•49 
9-0 
1-47 
1-37 
40 
•0007 
•00085 
•00059 
•00055 
Light . 
•59 
•49 
8-0 
•74 
•89 ’ 
50 
•0012 
•0010 
•00023 
•00029 
These linear growth coefficients can be compared, showing in Table II 
the relation between the root and shoot growth in the day and night 
