142 MEDULLOSEAE [CH. 



face, and there are said to be two seeds attached to the sides 

 of each pedicel (fig. 434). The oval seeds appear to be platy- 

 spermic and resemble Samaropsis fluitans Daws. Two of the 

 strobili figured by Kenault are attached at right angles to a 

 second axis, a habit suggesting comparison with that of a large 

 compound frond. Renault is inclined to regard these fertile 

 shoots as cycadean and suggests a possible connexion with the 

 Permian stems Ptychoxylon or Poroxylon, both of which are known 

 to have produced fairly numerous branches. In habit the spikes 

 are similar to some of the longer examples of Cordaianthus, but 

 their preservation is not sufficiently good to afford accurate 

 information as to the relation of seed to sporophyll. Strobilites 

 Milleryensis is, perhaps, more likely to be the fertile branch of a 

 compound frond of a Pteridosperm, and it is significant that the 

 seeds have been found in association with Callipteris leaves. 



COLPOXYLON. Brongniart. 



Colpoxylon aeduense Brongniart. The genus was founded by 

 Brongniart 1 on a piece of stem 15 cm. in diameter from the 

 Permian of the Autun district and regarded by him as a distinct 

 type, with certain resemblances to recent Cycads. A thick section 

 in the British Museum, 13 cm. in diameter (fig. 435, A), illustrates 

 the main anatomical features described by Renault 2 , to whom 

 our knowledge of the genus is chiefly due. There are two large 

 steles of irregular outline closely resembling those of Medullosa 

 Leuckarti (cf. fig. 416, H) ; each consists of a band of secondary 

 xylem with broad medullary rays and a narrow zone of phloem 

 enclosing a central region composed of parenchyma, in which 

 strands of primary tracheids, both reticulate and spiral, pursue 

 a more or less horizontal course, associated with a few small groups 

 of vertical xylem-strands at the inner edge of the secondary 

 wood. The manoxylic nature of the wood is clearly shown in 

 fig. 436 ; the continuous ink-line marks the position of the cambium 

 and the dots show the internal protoxylem. Homogeneous 

 parenchyma surrounds the steles and beyond this is crushed 

 tissue containing large secretory canals and nests of stereome 



1 Brongniart (49) A. p. 60. 



2 Renault (96) A. p. 299; (93) A. Pis. 66, 67. 



