EFFECT OF TEMPERATURE ON GROWTH. 83 1 



When De CandoIIe'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 — 



in 2 X 48 hours 

 48 

 48 

 48 

 48 

 48 



Koppen obtained the following growth in length of roots in periods of forty-eight 

 hours : — 



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 Wiirzburg'. 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 ungiinstigen Einfluss auf dass Wachsthum? 

 Arb. d. bot. Inst, in Wurzburg, Bd. I, 1874. 



