560 History of the Doctrine of [BOOK in. 



tion of growth at the internodes may vary very greatly, and 

 even Hunter's measurements in growing internodes in 1841 

 and 1843, and Grisebach's in 1843 led to no appreciable 

 result, because the observers neglected to apply the figures ob- 

 tained to the theory of the subject. It seemed to be generally 

 supposed that it was enough simply to write down the measure- 

 ments in figures, and that a theoretical result would spring 

 into being of itself; on the contrary the real scientific work 

 begins after the figures are obtained. The same cause pre- 

 vented the observations which have yet to be mentioned from 

 producing real fruit. The influence of the variability of the 

 temperature of the air \ and of the alternation of daylight and 

 darkness on the longitudinal growth of internodes and leaves 

 after they have emerged from the bud-condition, had often been 

 investigated; Christian Jacob Trew published in 1727 long- 

 continued daily measurements on the flowering stem of Agave 

 Americana in conjunction with observations on temperature 

 and weather ; a hundred years later similar observations were 

 made by Ernst Meyer in 1827, by Mulder in 1829, and by Van 

 der Hopp and De Vriese in 1847 and 1848; but Harting in 

 1842 and Caspary in 1856 were the first who went at all deeply 

 into the questions involved. These observations, some of 

 which were carefully made, led to no further result than the dis- 

 covery of the fact, which Miinter indicated and Harting applied 

 to theoretical purposes but which no one else thought worthy 

 of attention, namely that the rate of growth increases at first 



^jAt 



and independently of external causes, till it reaches a maximum, 

 and then decreases till at length it comes to an end ; they did 

 not even establish a really practical method of observation. 

 Scarcely two observers arrived at the same result, because the 

 questions respecting the relations of growth in length to tem- 

 perature and light had not been clearly and distinctly put. Com- 

 munications were published in the periodicals, which simply 



1 See ' Arbeiten des botanischen Institutes in Wtirzburg,' vol. i. p. 99. 



