158 



SCHIZAEACEAE 



[CH. 



Fig. 442. Transverse section of the stele and inner 

 cortex from the rhizome q{ Lygodiiim dichotoiiium. 

 ( X so. ) (? = endodermis; /i/2= phloem; j; = xylem. 

 (After Boodle.) 



are no adaxial hooks, while the xylem of the two sides of the curve is com- 

 pletely fused. This is probably a derivative form from the more usual 

 C-shaped type: in fact it may be held as condensed in relation to the 

 climbing habit (Gwynne-Vaughan, Ann. of Bot. p. 495, 1916). 



In stems of young plants of ScJiizaea or Anemia there is at the very base 

 a small protostele with a solid core of tracheides, and without parenchyma. 

 But sooner or later a mass of parenchymatous cells is found to occupy the 

 centre of a ring of tracheides, and the state may be described as solenoxylic 

 (Fig. 443, iii of Anemia, and vi of Schizaea). From this ring of xylem a 

 sector may pass to each leaf, opening a xylic gap, and with its phloem it 

 passes off as a foliar trace (Fig. 443 iv of Anemia, and v of Schizaea^, but 

 without any opening of the endodermis. In the adult stem of a large 

 ScJiizaea (S. dichotoma^, an approach is seen to a more complex state, but 

 without attaining to a settled solenostely. Fig. 444 shows a reconstruction 

 of such a stem by Dr J. M. Thompson. The central column is sclerotic pith, 

 in which occasionally an endodermal island, or a tract showing tracheid- 

 structure, may be seen (near top of figure). Shallow endodermal pockets of 

 very unequal depth occur at the foliar gaps, but do not constitute by their 

 connection any continuous inner endodermis. The stelar structure found in 

 this stem suggests a tentative upgrade advance, in a primitive type of Fern, 

 from a protostelic towards a solenostelic or a dictyostelic structure. Essentiall}' 

 similar details have been observed in other species, showing that this irregular 

 state is normal for the genus. Since tracheides have been seen in the 



