148 



PHILOSOPHICAL NOTES ON 



7. In the potato leaf, between the pairs of opposite leaflets, there 

 are pairs of smaller leaflets. The latter are opposite or alternate 

 if the former are opposite or alternate, and sometimes they are 

 altogether wanting. I think this disposition would admit of being 

 explained as follows :— The potato leaf descended from a bipinnate 

 leaf, the intermediate (c) being the secondary leaflets left behind by 

 the extension of the midrib. The two diagrams, Figs. 33 and 34, 

 will explain what I mean : (h) are the secondary leaflets of {a), (c) 



a 



^/^ 



l^'^ct 



Fig. 33. Diagram of potato leaf. 



\d 



d 



Fig. 84. Diagram of leaf from 

 which it may have descended. 



the same, left behind by the extension of the midrib. In other 

 instances (c) would have disappeared altogether, or become atrophied 

 into simple stipels. 



8. This mode of reasoning is not entirely without foundation, for 

 Dimorphanthus mandschuricus , with a bipinnate leaf, has a pair of 

 Bessile leaflets on the midrib at the emergence of each pair of 

 pinn», as shown in the accompanying diagram (a) Fig. 35 : (a) are 



Fig. 35. 



