:HAP. x The Problems of Growth 447 



ind hyponasty to express these relations. Darwin pointed 

 jut in 1880 that these phenomena really constitute a very 

 >low rhythm of nutation, and Vines in 1886 described 

 nany instances of this rhythm ; Darwin pointed out that 

 n the case of the hypocotyledonary axis it is of great 

 ise in the processes of germination, helping the seedling 

 :o emerge from the seed coats and to make their way 

 :hrough the soil. Wortmann pointed out similar purposes 

 .n the case of epicotyls in 1882. Wiesner described a 

 nodified form of epinastic growth exhibited by the epi- 

 :otyl under the term undulating nutation in 1883. Sachs, 

 ^Vortmann, and Vochting, showed that these modified 

 lutations of the axis of the seedling are spontaneous and 

 lot dependent upon gravitation. In 1886 Vines reaffirmed 

 the rhythmic character of epi- and hyponastic growth. 



The normal conditions of growth and their relation to 

 external stimulation were discussed by Sachs in 1863, and 

 it some length by Pfeffer in 1893. The influence of light 

 ipon them has been the most studied. We have seen that 

 i daily periodicity of growth in length was noticed by 

 several observers. A similar rhythm has been detected 

 n the case of growth in thickness. It was first observed 

 3y Reinke in 1876, and later by Friedrich in 1897. Prantl 

 n 1873, and Stebler in 1878, showed that the leaves of 

 nany plants show a daily periodicity of growth ; Kraus, in 

 [880, observed the same thing in the case of certain fruits 

 ind of various fungi ; while McMillan, in 1891, and Golden, 

 n 1894, detected a similar periodicity in the growth of 

 the tuber of the potato. 



Pfeffer suggested that these periodicities may have been 

 ; nduced by the alternation of day and night. A certain 

 :orrespondence between the two phenomena appeared 

 from the investigations of several botanists. In 1866 

 Duchartre found that the growth in length of various 

 shoots is greater during the night than during the day. 



