SPIRAL TORSION. 



321 



the Linnean Society,' March 6, 1855, vol. ii, p. 370). 

 The stem was distended, and hollow, and twisted on 

 itself; its fibres, moreover, were ar- 

 ranged in an oblique or spiral direc- 

 tion; the branches or leaf-stalks, which 

 usually are arranged in an opposite and 

 decussate manner, were, in this case, 

 disposed in a linear series, one over 

 the other, followng the line of cur- 

 vature of the stem. When the course 

 of the fibres was traced from the base 

 of one of the stalks, upward around 

 the stem, a spiral was found to be 

 completed at the base of the second 

 stalk, above that which was made 

 the starting point. Now, if opposite 

 leaves depend on the shortened con- 

 dition of the internode between the 

 two leaves, then, in the teazel-stem 

 just described, each turn of the spiral 

 would represent a lengthened inter- 

 node ; and, if the fibres of this speci- 

 men could be untwisted, and made to 

 assume the vertical direction, and, at 

 the same time, the internodes were 

 shortened, the result would be the 

 opposition of the branches and the 

 decussation of the pairs; this expla- 

 nation is borne out by the similar 

 twisting: which takes place so fi'e- , , . .,. 



,-, '^ . ,, . n /-I 1- , ea stem of Lhpsaeua 



quently m the species or tralium and ftUlonum. 

 other Buhiacece. 



G. Franc^ was one of the first to notice this twisting 

 in Galium, and M. Duchartre,'^ in mentioning a similar 

 instance, gives the following explanation of the appear- 

 ance which will be found to apply to most of these cases. 

 In the normal stem of Galium Mollugo the branches 



* Ephetn. Nat. Cur.,' dec. 2, ann. 1, 1683. p. 68, fig. U. 

 s ' Ajin. des Scienc. Nat.,' third series, vol. i. 184-t, p. 291. 



21 



Fig. 172. Twist- 



