XI THE HOMOSPOROUS LEPTOSPORANGIAT.-E 367 



fibres and cambiform cells, and in HeiiiipJilebiiun {Trichovianes) 

 Hookeri the phloem is absent from the very much reduced 

 smaller veins. This is possibly an intermediate condition 

 between the normally developed bundles of the veins of most 

 species and the so-called pseudo-veins, in which there is no 

 tracheary tissue developed, but which in their origin correspond 

 to the ordinary veins. The petiole always has a single vascular 

 bundle, usually of typical concentric structure, but in the section 

 HemipJilebiuvi Prantl ^ states that it is collateral. The ground 

 tissue of the petiole is largely composed of sclerenchyma like 

 that of the stem. 



The Roots 



The development of the roots has been studied only in a 

 very few forms. Bower " states that in T. radicans and H. 

 demissum it " conforms to the normal type for the root of 

 leptosporangiate Ferns, as described by Nageli and Leitgeb," 

 but does not go into details, and Prantl ^ makes an equally 

 brief statement. While lateral roots are completely wanting in 

 the section HemipJdebiuni, where their place is taken by leafless 

 branches, in most of the other forms they are developed in 

 considerable numbers. There is, according to Prantl,^ great 

 variation in the arrangement of the parts in the vascular 

 cylinder. Thus while all the species of HyinenopJiylhun have 

 diarch bundles, that of TricJioinancs pyxidiferinn is monarch, 

 while in one species, T. brachypus, as many as nine primary 

 xylem masses were found. The Marattiaceae alone, among the 

 other Ferns, show this great variability. 



Trichomes occur, but not so abundantly as in most of the 

 Leptosporangiatae. They have mostly the form of hairs, which 

 are either tem.porary (those formed on the margins of the young 

 leaves) oP persistent for a longer time, like those that cover the 

 end of the stem apex and bases of the petioles in many 

 species. 



TJie Sporangium 



All of the Hymenophyllaceae agree closely in the position of 

 the sporangia, whose development has, however, been studied 

 only in TricJiomanes ; but from the close correspondence in 



1 Prantl (i), p. 26. - Bower (11), p. 30S. 



3 Prantl (i). ^ Prantl, I.e. 



