CHAP. X. DIAGEOTKOPISM. 521 



namely, " transverse-geotropism," or diageotropism, as 

 we may call it for the sake of matching our other 

 terms. Under the influence of gravitation certain 

 parts are excited to place themselves more or less 

 transversely to the line of its action.* We made no 

 observations on this subject, and will here only re- 

 mark that the position of the secondary radicles of 

 various plants, which extend horizontally or are a 

 little inclined downwards, would probably be con- 

 sidered by Frank as due to transverse-geotropism. 

 As it has been shown in Chap. I. that the secondary 

 radicles of Cucurbita made serpentine tracks on a 

 smoked glass-plate, they clearly circumnutated, 

 and there can hardly be a doubt that this holds 

 good with other secondary radicles. It seems there- 

 fore highly probable that they place themselves in 

 their diageotropic position by means of modified 

 circurnnutation. 



Finally, we may conclude that the three kinds of 

 movement which have now been described and which 

 are excited by gravitation, consist of modified circurn- 

 nutation. Different parts or organs on the same plant, 

 and the same part in different species, are thus excited 

 to act in a widely different manner. We can see no 

 reason why the attraction of gravity should directly 

 modify the state of turgescence and subsequent growth 

 of one part on the upper side and of another part on 

 the lower side. We are therefore led to infer that both 

 geotropic, apogeotropic, and diageotropic movements, 

 the purpose of which we can generally understand, 



* Elfving has lately described excellent instance of such move- 

 ''Arbtiten des Bot. instituts in menls in the ihizomes of certain 

 Wurzmirg.' 13. ii. 1880, p. 4s9) an plants. 



