XXXVIIl] 



PTERIS 



53 



pensation-strand (Fig. 617). But a much more elaborate structure is seen in 

 P. '^Litobrochia) podophylla Svv. Here the stock is conical enlarging upwards 

 from the sporeling, and the vascular com- 

 plexity increases with its size (Fig. 618). At 

 the base it is protostelic (i) ; then follow the 

 states of medullated protostele and soleno- 

 stele (iii, iv): but soon an encroachment of 

 vascular tissue appears from the inner surface 

 of the solenostele, which provides the com- 

 pensation strand for the next leaf-gap (iv). 

 From this point onwards there is a continuous ^'S- Oil. P/ens [Utobrochui] Kuuzawa 



^ _ Ag. \ = F. elata,\2it. KarstemanaWzn.). 



medullar)^ system. The next step is the ex- Diagram showingthevasculartisiue at the 



r ,\ J 11 i J • ,*- „^ , J insertion of a leaf. A piece is supposed to 



pansion of the medullary strand mtoa second ^e cut out of the side of the solenostele, 



ring, and this is repeated again as the stock so as to show the internal vascular system. 

 . ,, . . , . ^T-i I • (After Gwynne-Vaughan.) 



mcreases rapidly m size (v). The result in 



the largest stock examined was as shown in Fig. 618 (vi), where there are 

 three concentric solonosteles, with a central strand suggesting the initiation 

 of a fourth. The similarity is obvious between this and what has been seen in 

 Thyrsopteris (Vol. II, Fig. 528), and in Saccoloma (Vol. II, Fig. 538). But the 



Fig. 618. A series of transverse sections of the stem of Fteris {Litobrochia) 

 podophylla Sw. , all drawn to the same scale. They show the great increase 

 in stelar complexity as the conical stem expands upwards. ( x 4.) The stelar 

 tracts are shaded. 



