THE FOSSIL OSMUNDACE^E. 763 



that the production of scale-leaves was initially due to certain adverse external conditions 

 which so reduced the vegetative energy of the plant that certain of the leaf-rudiments 

 were unable to attain their full development as foliage-leaves. That these abortive 

 leaves have acquired protective and storage functions is a secondary and an incidental 

 phenomenon. 



The Root. 



Numerous roots run in all directions through the cortex of the stem and through the 

 coating of leaf- bases (r. in PI. I., fig. 2, and PI. III., figs. 15-16). They bore their way 

 through the stipular wings of the leaf-bases, but are unable to perforate the sclerotic 

 rings. They arise upon the leaf- traces after the latter have become free from the stele of 

 the stem — one from each margin of the leaf-trace (PI. II., fig. 13, r.). No case was found 

 in which the xylem of the root was directly inserted upon that of the stem. Their 

 xylem strand was diarch in every case observed. The roots obtain a cortex of their own 

 while passing through the outer cortex of the stem (r. in fig. 2, PI. I.). At first it 

 consists of a thin- walled inner and a sclerotic outer zone, but in the peripheral region of 

 the fossil it appears to be all thin-walled. 



Osmundites Gibbiana, n.sp. 

 Plate III., figs. 17-19, and Plate IV., fig. 20. 



The single specimen of Osmundites Gibbiana that was found had the form of a 

 small oval disc measuring 4*5 by 5 cm. in diameter and slightly under 2 cm. in thick- 

 ness (PL III., fig. 17). It consisted of a portion of the stem of the plant surrounded by 

 a thick coat of compacted leaf-bases. Before mineralisation took place, the softer tissues 

 of the leaf-bases in the immediate neighbourhood of the stem had somewhat decayed, 

 causing this part of the fossil to sink inwards and produce a shallow circular trough 

 surrounding the stem, which projected from the centre of the fossil as shown in the 

 figure. The specimen was found loose, but Mr Dunlop, who was present when it was 

 discovered, assures us that there can be no doubt that it came from the same bed as 

 Osmundites Dunlopi. The stem itself is about 1*5-1 "7 cm. in diameter, and its external 

 limit lies about the point marked a in fig. 18, PI. III. In close proximity to the stem 

 the ensheathing leaf-bases are very tightly packed, but further out they become 

 gradually larger and more distinct, the outermost of all being more or less triangular 

 in section. The state of preservation is much the same as in Osmundites Dunlopi. 



As seen in section, the axis of the stem is occupied by a fairly wide space represent- 

 ing the pith, which is surrounded by a ring of xylem still well preserved. The inner 

 cortex and the peripheral tissues of the stele were greatly decayed before fossilisation, 

 but the fibrous sclerotic elements of the broad outer cortex (o.c, fig. 18, PL III.) were 



