XLV] 



PLATYCERIUM 



207 



system of receptacular xylem gives rise to the "diplodesmic" structure. 

 These features serve to Hnk Cheiropletiria with a number of more modern 

 types of Ferns, some of which will now be described and compared. The first 

 of these will be the remarkable Stag's Horn Ferns, of the genus Platycermm. 



Fig. 717. Sporangia of Cheiropleuria. a — (/show various aspects of the spo- 

 rangium, with its 4-rowed stalk, and relatively large capsule and continuous 

 oblique ring, e shows part of a sorus cut transversely to the sporangial stalks. 

 These are shaded, while the hairs are left clear. ( x 80.) 



PLATYCERIUM Desvaux, 1827. 

 This genus owes its systematic permanence to the very distinctive vege- 

 tative characters which it presents. The earlier systematists, though linking 

 it with AcrosticJnivi ,'a.f^^Q:d.x to have regarded Platyceriiini as an isolated and 

 bizarre phenomenon. Even in later times Diels has remarked that "the 

 genus stands quite isolated among the Polypodiaceae of the present day": 

 and he specifically states that Cheii'opleiiria has no near relation to it {Nat. 

 Pflanzenfain. i, 4, p. 339). More recently Von Straszewski concludes that 

 Platyceriuin does not belong to the Acrosticheae, nor does he hold it akin to 

 Dipteris or Cheiropleuria {Flora, 191 5, Bd. 108, p. 304). But Christ places 



