74 PEOTOPTERIS. 



preserved petiole bases of P. Witteana and those of Dicksonia 

 antarctica. 



Between the prominent petiole scars the matrix of the fossil is 

 somewhat lighter in colour, as at a. a., Figs. 1-3; this appears to 

 consist of elongated parenchymatous cells, which may possibly 

 have originally existed as multicellular filaments, but have 

 been more or less welded together in the process of mineralization. 

 Here and there in this inter-petiolar tissue traces of adventitious 

 roots occur, as e.g. at r and r f in Figs. 1-3. 



In Dicksonia antarctica the bases of the petioles are separated by 

 a woolly mass of brown threads, traversed by a few adventitious 

 roots. If these threads (ramenta) be examined microscopically 

 they are found to be made up of long and narrow parenchymatous 

 elements, very similar in shape to those which occur between the 

 petiole bases in the fossil stem. 



In PI. XI. Fig. 2 a transverse section of the fossil stem is repre- 

 sented natural size ; the curved band-form vascular plates are 

 clearly shown at t, and at p portions of the conducting tissue are 

 curving outwards as leaf-traces ; an impression of a root section is 

 seen at r, and at a are the masses of tissue separating the individual 

 petioles. 



A small piece of the vascular tissue of the stem is shown in 

 Pig. 4 ; the xylem, x, is made up of polygonal tracheides of the 

 scalariform type, and associated with these there are indications 

 of parenchymatous cells ; the whole xylem tissue being apparently 

 very similar in structure to that in the stem of Dicksonia antarctica. 



The dark lines, b.b, on either side of the xylem no doubt mark 

 the limits of the phloem, but this more delicate tissue has not been 

 preserved. 



In a few places there are traces of fairly large brown-walled 

 elements external to the limits of the phloem. 



The xylem of this specimen, as regards the arrangement of 

 the vascular bands and their histological structure, is very 

 similar to that of Protopteris Cottai as figured by Corda. 1 



V. 2181. An imperfectly preserved Sandstone cast. Leaf-scars 

 indistinctly shown. Ecclesbourne. Rufford Coll. 



1 Flor. Vorwelt. pi. xlix. 



There is a section of P. Cottai in the Botanical Department Collection (British 

 Museum) cut from the specimen figured by Corda. 



