xix] 



HABIT 



53 



In Lobb's specimens of O. intermedium (Hook, Ic. PI. 995), as well as in Campbell's more 

 recent collection {Eusp. Ferns, 191 1, PI. 4, A), the sterile lobe is still present though some- 

 times almost obsolete. The facts suggest that in certain derivatives from O. pe?tdulum 

 which have forsaken epiphytism for a soil-habit, mycorhiza present in them all has been 

 advanced to be the main source of food, with reduction of the sterile blade as the result. 

 Such departures as these from the usual type are best interpreted as secondary, superposed 

 upon a type already standardised in the form held as normal for the genus. Taken together 

 with the reticulate venation universal for the genus, they mark Ophioglossum not as the 

 most primitive, but probably the most advanced of the three genera. Anatomy also sup- 

 ports this view. 



at 2!L. 



ComaL ■ 



Fig. 346. Longitudinal section through 

 a leaf-insertion of Helniinthostachys 

 showing the petiole [pct^ and stipule 

 {st. ), in the axil of which a canal arises 

 leading obliquely down to a dormant 

 bud. (After Gwynne-Vaughan.) 



Fig. 345. OphioglossiDii simplex 

 Ridley, slightly reduced. Three 

 leaves are seen inserted on a 

 short stock, but the leaves 

 appear to consist each of a 

 fertile spike, with no sterile 

 lamina. 



