304 R. H. Compton. 
As we pass along the petiole the bundle as a whole narrows 
somewhat by the disappearance of much of the central parenchyma. 
The xylem elements are reduced in number, but the brown fillings 
of the lumina, present in the base of the petiole, are absent further 
along. 
The lamina presents no structural features of peculiar interest. 
It may, however, he noted that the curious projections of the walls 
in the lower epidermis present in M. pectinata (Seward, 9, p. 181) 
are also found in M. sannentosa. 
Morphology of the Frond. 
The complicated branch system of the frond may readily be 
related to a primitive type in which a series of dichotomies occurs : 
Fig. 40. Diagram representing the mode of branching of the frond. The 
letters indicate the order of the branches to which they are affixed, the same 
number of dashes being given to each of the two branches arising by a single 
dichotomy. 
