454 The Physiology of Plants BOOK in 



Batalin, in the year 1873, associated the rise and fall of 

 certain foliage leaves with the changes of growth, and sug- 

 gested that pulvini act in the same way. In 1875 Pfeffer 

 showed the true nature of the action of pulvini, and gave 

 a full account of their structure. In 1876 he proved that 

 the nocturnal rhythm is induced by the periodicity of 

 stimulation of day and night, and showed that temperature 

 as well as light is concerned in the phenomena. Pfeffer 

 denied that the daily rhythm is hereditary. 



Darwin, in 1880, added many instances of plants showing 

 this rhythm to those previously examined. 



An effect of a similar nature was studied by Cohn in 

 1859, Batalin in 1871, and Pfeffer in 1873. They found 

 that if a plant of Oxalis acetosella is brought suddenly 

 from a dull light to brilliant illumination, the leaves fall 

 as they do in darkness. 



The influence of temperature on growth and movement 

 was studied by many of the older writers, to whom we 

 owe the discovery of the fact that growth is only possible 

 between certain limits, which range, however, between the 

 freezing-point and about 50 C. Somewhere between these 

 points an optimum temperature is found, which varies 

 considerably for different plants. The subject of this 

 relationship was investigated very fully by Sachs in 1860, 

 and later, in 1870, it received considerable attention from 

 Koppen and from De Vries. More recently investigations 

 have been made by numerous observers, who from reasons 

 of space cannot be quoted here. A full resume of the 

 literature is given by Pfeffer in his Pflanzenphysiologie, 

 Eng. ed. (1903), vol. ii, p. 83. 



Koppen found that frequent and considerable variations 

 of temperature cause retardation of growth ; it was shown 

 however, by Pedersen, in 1874, that to bring this about 

 the upper limit of these variations must be considerably 

 higher than the optimum temperature for the plant under 



