264 



DICKSONIACEAE 



[CH. 



(Fig. 532). The point of disintegration of the meristele varies: it is clearly 

 an advance upon what is seen in Thyrsopteris. There are no accessory- 

 strands in the pith or leaf-stalk. Where the stem is upright or dendroid 

 as it is in Dicksonia antarctica, the stelar structure is similar, but more 

 complicated by the dense insertion of the leaves. It becomes thus a highl)' 



Fig. 530. Illustrations of the sori of Dicksoniaceae. A —Balantiziiii Cukita (L'Her.) Kaulf.: part of 

 a pinnule of third order. B-D = Dicksonia arborescens L'Her.: j9 = lo\ver part of a pinna of the first 

 order; C= pinna of the second order; Z> = sorus with indusium. E, F= Cibotitim Baronietz Link: 

 ^ slower part of a pinna of first order; /^=part of a segment with two sori. (From Engler and 

 Prantl. /?-/^ after Hooker.) 



Fig. 531. Transverse section of the Fig. 532. Cilwtium Barometz. Portion of the vascular 

 solenostelic rhizome of Cibotiiini system of the stem, seen from within, and showing the 

 Barometz {V..)'^. Sm. (Natural size.) departure of three leaf-traces. (After Gwynne-Vaughan.) 



elaborated dictyostele, but with very narrow and short leaf-gaps (Fig. 533). 

 It is further complicated by the deeply sinuous corrugations of the stele, and 

 of the sclerotic sheaths that invest it internally and externally (compare Vol. I, 

 p. 196, Fig, 184). Doubtless this is a source of additional mechanical strength, 

 but it also gives greatly increased surface-area to the vascular system, and 

 particularly to the xylem. The pith is of unusual size, three inches or more 



