XXXVIII] PTERIDEAE-PTERIDINAE 6i 



■ Pteridhim Gleditch (1760) ... ... ... ... i species. 



Hairs only are borne: vascular system highly disintegrated : venation 

 open: bi-indusiate: receptacle marginal: sporangial succession at first 

 gradate, later mixed. 

 Prt^i-zd: St Hilaire (1833) ... ... ... .. 7 species. 



Hairs only: solenostelic : leaf-trace undivided: venation open: bi- 

 indusiate, but lower indusium inconstant: receptacle marginal (?): 

 sporangial succession gradate to mixed. 

 Lo7tchitis L. (1753) ... ... ... ... ... 8 species. 



L. aurita L. Hairs only: venation coarsely reticulate: solenostelic, 

 with occasional perforations: leaf-trace binary: lower indusium re- 

 placed by hairs: sporangia mixed. 



L. hirsuta L. Hairs and scales : venation open : large solenostele with 

 occasional perforations : leaf-trace binary : lower indusium replaced by 

 hairs: sporangia mixed. 



Histiopteris (Agardh) J. Smith (1875) 2 species. 



Hairs and scales: venation occasionally reticulate : solenostelic (corru- 

 gated): leaf-trace undivided at departure: lower indusium absent: 

 receptacle intermediate between marginal and superficial: sporangia 

 basipetal at first, later mixed. 

 P/^m L. (1753) ... ... ... ... ... 157 species. 



(i) Eu-Pteris Newman. Scales: leaf-trace divided: venation open: 

 lower indusium absent: receptacle superficial: sporangia mixed. 

 (ii) LitohrocJiia Presl. Scales: reticulate venation, with no free vein- 

 lets: solenostelic, with medullary system, and undivided leaf-trace: 

 lower indusium absent : receptacle superficial and widened : sporangia 

 mixed {L. podopJiylla Sw.). 

 Acrostichuin L. (1753). Scales: reticulate venation: solenostelic to dictyo- 

 stelic,with medullary system: leaf-trace soon divided: indusium absent: 

 receptacle superficial, covering part {^A. praestantissimwn Bory) or 

 the whole of the space between margin and midrib (^A. aiireuni L.), 

 The sequence of genera thus quoted may not actually represent a simple 

 phyletic line. The fact that the changes of detail do not all march parallel, 

 one with another, makes such simplicity appear improbable. But the pro- 

 gressive sweep from solenostely to disintegration : from hairs to scales : from 

 open venation to reticulate: from marginal sori to superficial: from bi- 

 indusiate to uni-indusiate: from gradate sori to mixed: from a convex 

 receptacle to one flattened and extended over the leaf-surface, forms a body 

 of evidence that leads finally to the state of Acrostichuin aiirciim. The stelar 

 evidence appears less conclusive \i Pteridiinn be held as a starting-point: 

 but it is an exceptional plant in many ways. If, however, the smaller species 



