

THE FOSSIL OSMUNDACE^E. 659 



ably according to the level at which the section is taken. In the outermost petioles 

 (fig. 43, int. sol.) the leaf- trace is immediately surrounded by a broad zone of dense 

 sclerenchyma. Then conies a wide belt of thin-walled tissue (fig. 43, i. par.), and 

 then the customary petiolar sclerotic ring, which is here comparatively narrow (sc. /.). 

 The sclerotic ring is in turn enveloped by several layers of thin-walled parenchyma, 

 which maintain the rhomboidal outline of the sclerotic ring and are not prolonged at 

 the sides into stipules. A peculiarly interesting feature of the petioles of Bathyp- 

 teris is the presence of numerous slender spine-like outgrowths from their periphery, 

 which project upwards into the spaces between the petioles and attain a considerable 

 length. In petioles nearer the stem the inner sclerotic tissue in contact with the 

 leaf-trace increases greatly in amount until it entirely fills up the concavity of the 

 trace (fig. 44) and replaces almost completely the parenchyma lying between it and 

 the sclerotic ring (fig. 45). This internal sclerenchyma follows the leaf- trace right 

 into the stem undiminished in quantity, and is here separated from the outer sclerotic 

 cortex of the stem only by a very few layers of parenchyma. 



The constituent elements of the sclerenchyma differ considerably in the nature of 

 their preservation. Those of the petiolar sclerotic rings are mostly well preserved, with 

 almost homogeneous brown walls. So also are some of those of the inner sclerenchyma 

 in contact with the leaf-trace ; the walls of these elements being exceptionally thick 

 and more or less distinctly stratified. In most of them, however, the layers of 

 stratification have become separated as though they had been macerated, and the 

 thickness of the wall is occupied by a number of narrow black concentric lamellae 

 alternating with broader and lighter-coloured bands (figs. 46 and 47). The lumen is 

 almost obliterated, and is frequently filled by a small dark mass. In transverse section 

 they have a rounded outline with small triangular intercellular spaces at the corners, 

 while in longitudinal section they are shortly rectangular and blunt ended. The 

 elements of the outer sclerotic rings are narrower and fibrous, and they also have 

 small intercellular spaces at the angles. 



As already stated, the periphery of the petiole is beset on all sides by spinose 

 emergences which grow upwards parallel to the petioles in the spaces that lie between 

 them. In a transverse section of the petiolar coating these spaces are almost com- 

 pletely filled up by the transverse sections of the numerous spines. The best 

 preserved of these show that the centre of the spine is occupied by a stout strand of 

 narrow cells with thick and usually lamellated cell-walls, which are surrounded by two 

 or three layers of larger thin-walled cells (figs. 49 and 50). In longitudinal section the 

 sclerotic cells are seen to be fibrous, while their thin-walled envelope is parenchymatous 

 (fig. 52). In most of the spines, however, the more delicate outer layers have become 

 decayed or worn away, and the sclerotic core alone is left (figs. 49 and 51) ; and in many 

 of them the central elements even of the sclerotic core have disintegrated, leaving a 

 small black mass of carbonaceous matter or simply an empty space (fig. 51). On account 

 of the great variation in size of the transverse sections of the spines it would seem that 



TRANS. ROY. SOC. EDIN., VOL. XL VI. PART III. (NO. 23). 96 



