49 
1914-15.] Studies on Periodicity in Plant Growtli. 
periods, under all four conditions, and in Table III the relative amounts 
of growth during the day and night periods in root and shoot respectively, 
under all the conditions. 
Table II. 
Winter. 
Summer. 
Day. 
Night. 
Day. 
Night. 
Root : Shoot. 
Root ; Shoot. 
Root : Shoot. 
Root ; Shoot. 
Normal 
' 3-5 : 1 
3 : 1 
3-2 : 1 
3-6 : 1 
{a) Intermittent 
3-7 : 1 
5 : 1 
2-8 ; 1 
2-8 : 1 
{b) Dark . 
1-6 : 1 
2-3 ; 1 
IT ; 1 
1-5 : 1 
(c) Light . 
2-5 : 1 
2-6 : 1 
5-2 : 1 
3-3 : 1 
General Results from Table II. 
1. Under ordinary conditions the root always grows more quickly than 
the shoot by day or night. 
2. Change of external conditions, such as — 
{a) Exposing the whole plant, root and shoot, to alternate light 
and darkness ; 
(h) Keeping the whole organism in continuous darkness, i.e. 
the case of etiolated plants ; 
(c) Keeping the whole plant in continuous illumination, but not 
of uniform intensity, substituting electric light during 
the night, 
affects this rate ratio, but never reverses it. 
3. Illumination accelerates the root rate the converse of the shoot 
rate. 
4. The rate ratios are affected by the natural seasonal changes — 
summer and winter. 
The relative rate is influenced by the seasonal change under {a), being 
increased in winter but lowered in summer. The relative growth rates 
tend more nearly to equality in etiolated plants (6), the root, however, still 
keeping the lead. This is due, of course, to the increased growth of the 
shoot when the relative discrepancy is made up. 
Under the converse conditions of constant illumination (c) the relative 
rates of root and shoot are diminished compared with the normal, except 
during the long summer day, when the ratio is very much increased, just 
as during the long winter night under (a), when it is also very much 
VOL. XXXV. " 4 
