130 THE MORPHOLOGY OF PTERIDOPHYTES 



only a few cm in diameter. The stele of most species was a 

 polycyclic dictyostele which, in the more complex types, 

 contained as many as eleven interconnecting coaxial 

 cylinders (or, rather, inverted cones fitting inside one 

 another). Each was dissected into a number of mesarch 

 meristeles completely surrounded by phloem, and the leaf 

 traces at any particular level arose from the outermost 

 system, while the inner systems were concerned with the 

 origin of leaf traces at higher levels. The earhest examples, 

 however, were simpler than this in their internal anatomy, 

 e.g. P. Renaultii from the Lower Coal Measures had an 

 endarch solenostele; and there is evidence that even the 

 complex Permian species had a relatively simple structure 

 near the base of the trunk, as would be expected by analogy 

 with present-day ferns. Although the trunks were widest at 

 the base, this was not because the stem within was wider 

 but because there were a greater number of rootlets in the 

 mantle; the stem v/as actually smaller towards the base. 

 Some species had the leaves arranged distichously, some in 

 three or four vertical rows, while others had them arranged 

 spirally, as in most modern representatives of the group. 



The Marattiales are represented at the present day by 

 about 200 species, placed in six (or seven) genera, most of 

 which are confined to the tropics. Angiopteris (lOO species) 

 is a genus of the Old World, extending from Polynesia to 

 Madagascar, while Danaea (thirty-two species) is confined 

 to the New World. Marattia (sixty species) is pan-tropical 

 and extends as far south as New Zealand. Christensenia 

 { = Kaulfussia) is monotypic and is confined to the Indo- 

 Malayan region. Most species have massive erect axes, but 

 they never attain the dimensions of the fossil Psaronius. The 

 largest, although reaching a diameter of i m, seldom exceed 

 this in height. Christensenia and some species of Danaea, 

 however, have creeping horizontal axes. The fronds of some 

 species are larger than in any other living ferns and may be 

 as much as 6 m long, with petioles 6 cm in diameter. They 



