74 Morphology BOOK i 



of sheath, petiole, and blade, or, to use his own terminology, 

 of hypo-, meso-, and epi-podium. 



Bower's theory differed considerably from that of Eichler. 

 According to the latter the leaf is a member which may, 

 or may not, branch in its upper region. Bower held it 

 to be a potential branch-system. Eichler distinguished 

 between the basal part of the leaf and the upper part, 

 with its potentiality of branching ; Bower distinguished 

 between the podium itself and its branches, if any. 



Bower's theory of the morphology of the leaf and stem 

 implied a much greater similarity between the two than 

 did the older ideas ; instead of a fundamental difference in 

 organization it suggested a tolerably close and detailed 

 resemblance ; both are branch systems, showing alike 

 axial and appendicular parts ; both are capable of flatten- 

 ing or winging, the process in each being adaptive, or 

 functional. 



Bower applied his theory only to the Pteridophytes and the 

 Gymnosperms, and supported it by anatomical researches 

 carried out on the growing points, and by the history of 

 the development of the individual leaf and of the separate 

 pinnae. 



The present writer in 1895 advanced the view that this 

 theory is applicable also to the Dicotyledons, and applied 

 it to leaves generally. Bower indicated that his opinion ran 

 in that direction, but he did not amplify it. The writer 

 showed that all cases can be explained by the theory of 

 a branching podium or axis, with a capacity for developing 

 wings, and pointed out the laws of branching are practically 

 the same as those affecting the stem. Also that the 

 capacity for winging is not peculiar to the leaf, but is 

 shared by the stem, and is therefore not a distinctive, or 

 inherent indication of difference of organization. On this 

 view the midrib and the other prominent ribs are axial parts, 

 branches whose wings have congenitally fused to varying 



