VIIl] 



POLYCYCLY 



155 



development corresponds essentially with that described byGwynne-Vaughan 

 for the Pterideae: but as the Matonineae are systematically far apart from 

 these, it appears that polycycly is homoplastic in two at least, and probably 

 in several other phyla. 



The very much disintegrated system of vascular strands found in Platy- 

 cerhnn aethiopicum may be referred to a state of polycycly combined with pro- 

 fuse perforation of the solenosteles (Fig, 149, 8). In the smaller P. alcicorne the 

 numerous meristeles are arranged in a simple circle, and a group of strands 

 passes off from them as a leaf-trace to each leaf (Fig. 149, 7). This seems to be 



Fig. 149. Series of solenostelic and dictyostelic stems of Ferns, all drawn to same scale. 

 ( X 2.) I, Metaxya; 2, Diptei-is conjiigata\ 3, Maionia pectinata\ 4, Plagiogyria 

 pycjiophylla; 5, Thyrsopteris elegans; 6, Saccolotna elegans; 7, Platyceriiim alci- 

 corne; 8, Platycerium aethiopicum. These drawings show that the disintegration of 

 the stele does not depend on absolute size alone. 



derived from a solenostelic state with many perforations, as commonly seen 

 in advanced Leptosporangiate Ferns. In the larger P. aethiopicum the very 

 numerous meristeles are disposed in irregular concentric circles, an arrange- 

 ment referable to a polycyclic state with profuse perforations (Fig. 149, s). 

 The extremely complicated vascular systems of the Marattiaceae and Psaro- 

 nieae may also be properly ranked as further examples of a high state of 

 polycycly, greatly disintegrated by perforation. Here they can only be 

 mentioned and reference given to Tansley's account of them {Lectiwes on 

 the Filicinean Vascular System, pp. 82-95), and to the reconstructions of 



