EFFECT OF TEMPERATURE ON GROWTH. 
When De Candolle's inferior limits are below 5° C, they are most probably correct ; 
his superior limits and temperatures of most rapid growth are, on the other hand, for 
the most part certainly too low. 
More accurate information is afforded by the figures which give the lengths attained 
by roots in equal periods of time at different temperatures, and express therefore the 
rate of the growth of the roots of seedlings at different constant temperatures. These 
numbers increase from the inferior limit to the temperature of most rapid growth, and 
fall again from it to the superior limit. 
In Zea Mais, for example, I found — 
Temperature. Length attained by the root. 
in 2 X 48 hours 17*1° C. 2*5 mm. 
48 26'2 24*5 
48 33-2 39-0 
48 " 34'o 55*0 
48 38*2 25*2 
48 42-5 5-9 
Koppen obtained the following growth in length of roots in periods of forty-eight 
hours : — 
Pisum sativum. Zea Mais. 
5-0° mm. 
8'3 I'imm. 
3o"o io*8 
53-9 29-6 
40*4 26*5 
38-5 64-6 
2 30 69-5 
8*7 20*7 
Temperature. 
Lupinics albus. 
i4-i°G. 
9*1 mm. 
180 
11-6 
5^3•5 
31-0 
26-6 
54-1 
28-5 
50-1 
30*2 
43*8 
33*5 
I4'2 
36-5 
12-6 
The following are De Vries' results, also in periods of forty-eight hours : — 
Temperature. Cucumis Melo. Sinapis alba. Lepidiu7n sativum, Linum usitatissimum. 
15*1° C. 3'8 mm. 5*9 mm. i*i mm. 
21'6 24*9 38*9 20'5 
27-4 1 8-2 mm. 52-0 71-9 44*8 
30*6 27*1 44*1 44*6 39'9 
33'9 38'6 30*2 26*9 28T 
37*2 70*3 io"o o*o 9*2 
The assertion made by Koppen, in support of which he brings forward an array of 
figures, that similar parts of plants grow at different rates at the same mean temperature, 
whether the mean temperature is constant or whether it varies above and below the 
mean, and further that the rapidity of growth is diminished by the variations of the 
temperature even when the variations take place below the optimum, was inserted in the 
third edition of this book. This assertion, however, has not been confirmed by the care- 
ful observations made in different ways by Pedersen in the laboratory at Würzburg \ We 
shall see in Sect. 26 that variations of temperature act as stimuli which affect the rapidity 
of growth of many foliage and floral leaves in a remarkable manner. A thorough inves- 
tigation of the subject from this point of view is much to be desired. 
as if burnt at 40° C, a phenomenon which has not been noticed by others. These 'burnt' seeds 
however germinated afterwards at a lower temperature. 
^ Haben Temperaturschwankungen als solche einen vmgünstigen Einfluss auf dass Wachsthum? 
Arb. d. bot. Inst, in Würzburg, Bd. I, 1874. 
