354 DR D. H. SCOTT ON THE 



2. Pitijs Withami (Lindl. et Hutt., sp.). 



I take this species to include the P. medullaris of Lindley and Hutton, which 

 Witham himself regarded as probably identical with the former.* There seems no 

 object in keeping up the two specific names, as the characters on which P. medullaris 

 was separated — the large pith, and the appearance of concentric markings (probably not 

 annual rings) in the wood, are common to many stems of the Dadoxylon group, and of 

 no diagnostic value. Both were included in the old genus Pinites of Lindley and 

 Hutton, which, as employed by those authors, has long since been abandoned. The 

 distinction drawn by Witham t between Pinites and Pitys, and based on the round, 

 separate pits in the case of Pitys, and the hexagonal contiguous pits in that of Pinites, 

 has no value, as both conditions are found, in different parts of the same specimen. 

 Pitys Withami is, in fact, a closely-allied species to P. antiqua. The pitting on the 

 tracheides is identical (if equally well-preserved specimens are compared), and there is no 

 constant difference in the size of the elements. The medullary rays are, however, on the 

 whole narrower in P. Withami than in P. antiqua, rarely exceeding four cells in width in 

 the former. The point of interest for our present purpose is that Pitys Withami shows 

 the same primary anatomical structure as P. antiqua, having, like that species, a ring 

 of primary xylem-strands disposed round the pith. My observations were made on an 

 original section of Witham's (figured in Internal Structure, PI. VI., figs. 5-8), lent me 

 by Professor Bayley Balfour. This section was from the branch to which Lindley and 

 Hutton gave the name of P. medullaris ; it is represented as a whole in PL II. phot. 10. 

 The pith, which measures 19 x 10 mm., shows essentially the same structure (so far as 

 exhibited in transverse section) as that of P. antiqua, but much of the tissue is altered in 

 appearance by the infiltration of some dark-brown substance. The preservation is 

 tolerably good, but towards the wood, where the cells become smaller, the structure is 

 obscure, partly owing to the section not being sufficiently thin. Yet at several places 

 small strands of thick-walled elements can be distinguished lying near the outer margin 

 of the pith, a little within the ring of secondary wood. These groups agree so closely, 

 in appearance and position, with the primary xylem-strands of P. antiqua, that we can- 

 not doubt their identical nature. The strand figured (PL VI. fig. 21) appears to be a 

 double one. 



The secondary wood is described by Witham (I.e., p. 32) as showing " decided indi- 

 cations of five concentric layers." The layers are marked by tangential bands of some- 

 what flattened elements (see Witham, PL VI., fig. 8)4 and the bands, so far as the 

 section extends, are fairly, though not completely, continuous. There is thus a certain 

 resemblance to the annual rings of recent Coniferse, but very much less marked and 

 regular in the fossil, so that (considering the inconstancy of such markings in Palaeozoic 



* Internal Structure, pp. 36 and 42. Pitys Withami was founded on the well-known Craigleith trees discovered 

 in 1826 and 1831 in the Craigleith Quarry, near Edinburgh. 



t Who, however, himself had some doubts as to the generic value of the distinction. L.c, p. 39. 



\ This figure gives a fair idea of the relative forms of the elements, but the dark shading makes the rings appear 

 more conspicuous than they really are. 



