45G R. KIDSTON AND D. T. GWYNNE-VAUGHAN ON 



have presented a diameter of 14 cm. at least. The softer tissues of the stele and cortex 

 were almost entirely destroyed before fossilization, and the sclerotic cortex which remains 

 has in consequence collapsed. It is, therefore, impossible to give exact measurements ; 

 but the stem itself, before it was compressed, must have been about 3 6 cm. in diameter. 

 The inner cortex was composed of thin-walled parenchyma, and was quite narrow, being 

 only 2 mm. wide in the fossil. The outer cortex consisted of fibrous sclerenchyma, and 

 attained a width of as much as 4-5 mm. 



The Structure of the Stele. 



The stele is very much flattened ; so much so, in fact, that the two sides of the 

 xylem ring are in some places actually in contact with one another (fig. 1 ). If it were 

 restored to its original form it would probably measure about 19 mm. in diameter. 

 The individual strands of the xylem ring show all the different variations in form 

 characteristic of the modern Osmundacew, and frequently several of them are more or 

 less joined together laterally to form continuous bands (fig. 2), as is also the case in 

 species of the modern genus Todea.* The xylem strands in the ring are very numerous, 

 amounting to as many as fifty-six. The xylem elements are fairly well preserved, 

 and consist of tracheae alone without any xylem parenchyma. The tracheae are of the 

 typical Osmundaceous type ; that is to say, the pits are actual perforations, and several 

 vertical series of them occur on each wall (fig. 3). They present the same appearance 

 in transverse section as those of Osmundites Skidegatensis (Part II., PI. II., fig. 7), only 

 they are much less perfectly preserved. As seen in longitudinal section the pits are 

 more or less oblong, and two to four series of them occur on each wall (fig. 3). The 

 tracheae decrease in size towards the outer margin of the xylem, but the same multiseriate 

 pits are seen throughout. The protoxylem elements alone have one series of pits, and 

 are typical scalariform tracheae. 



As regards the soft peripheral parts of the stele, the xylem sheath alone is fairly well 

 preserved at certain points. The phloem, pericycle, and endodermis are not recognisable 

 as such, but their position is occupied by a zone of a brown structureless substance. 

 If the endodermis had been well developed there is reason to believe that it would have 

 left some indication of its existence, for the cortical cells in immediate contact with the 

 stele have maintained their structure. 



The most interesting feature in the anatomy of Osmundites Kolbei lies in the con- 

 stitution of the central tissue of the stele occupying the position of a pith. Owing to 

 the flattening of the stele this pith is, for the most part, very much compressed ; but a 

 sufficient amount is still present at certain points to determine the fact that it did not 

 consist of a homogeneous tissue. Some of its constituents were so delicate that they 

 have completely disintegrated, and nothing can be made out as to their structure. It nlso 



* Skward and Ford, " Anatomy of Torlea, etc.," Trans. Linn. Soc. Lond., Ser. II., Bot., vol. vi., 1903, pi. xxix. fig. 29. 



