308 Longitudinal Symmetry in Phanerogamia. 



in Rhinanthus, in which the opposite phyllotaxis changed to alternate by a 

 process which some botanists would describe as one of the concrescence of the 

 two opposite leaves. 



The observations just mentioned, as well as some regarding displacements, 

 more or less clearly indicated than when phyllotaxis is cyclic in design, 

 alternate internodes, nodes, and associated displacements are more closely 

 correlated than are successive ones. This may imply that morphogenous 

 impulses travel along orthostichies, but it at least sheds light upon a number 

 of varied morphological problems. 



The theory of the construction of the phanerogamous stem is discussed, and 

 stress is laid upon the fact that the longitudinal displacement of leaves 

 demonstrates that internodes may be of different phylogenetic age and 

 lineage, and are, therefore, not serially homologous segments. The interpreta- 

 tion of these displacements adopted in this paper would also imply that the 

 stem is partly constituted of tissue originally appertaining to leaves, so that 

 " stem " and " leaf " are not sharply distinguished members. 



The graphic method was also tested by reference to other morphological 

 problems. It does not afford the means of distinguishing between a sympode 

 and a monopode in the cases of the sympodes of Petunia and Myosotis, though 

 the curves harmonise with the accepted view. But more decisive results were 

 obtained with the tendrilled axis of Ampelopsis hederacea ; here the complex, 

 periodic, yet apparently irregular, internode curve could be analysed only into 

 three consistent sub-curves (by joining every third ordinate) ; and this exactly 

 corresponds to the interpretation of structure adopted by Eichler and others, 

 while it directly conflicts with rival theories. 



