160 Mr Seward, Notes on the Binney Collection 



secretory element filled with dark contents, sweep across the 

 face of the tracheids. In the walls of some of the medullary-ray 

 elements there are indications of the existence of a few obliquely 

 oval simple pits 1 . The tracheids are characterised by multi- 

 seriate rows of contiguous bordered pits which cover their radial 

 walls. Section 1. 10 affords the best illustration of the structure of 

 the secondary xylem as seen in radial longitudinal section. 



The practical identity in structure of the secondary wood of 

 this stem with that of Lyginodendron robustum Sew. as figured in 

 vol. XI. of the Annals of Botany (PL v.) 2 renders it unnecessary to 

 illustrate its characteristic appearance by figures. Tn Lyginoden- 

 dron robustum (e.g. Section 1133 Williamson Cabinet, British 

 Museum) the medullary rays are slightly broader and more obvious 

 than in the plant under consideration ; but the difference is very 

 slight. The loose parenchymatous nature of the xylem agrees with 

 the characteristic structure of recent cycadean stems and with the 

 xylem of such fossil genera as Lyginodendron 3 , Heterangium 3 , 

 Medidlosa 4 , Colpoxylon 5 , and other Palaeozoic types. 



It is of interest to note the striking difference in the structure 

 of patches of the secondary wood, in which the more delicate 

 medullary-ray cells have been almost obliterated by compression, 

 as compared with the more perfectly preserved portions; in the 

 former the wood appears to be of the more compact coniferous 

 type, the loose cycadean character having been lost through im- 

 perfect preservation. 



2. Primary xylem. 



The wide primary stele of the stem presents certain features of 

 special interest which lead me to regard the plant as the type of a 

 new genus. The enlarged microphotograph reproduced in PI. VI. — 

 eight times the natural size — shows that the greater part of the 

 primary stele consists of groups of unusually large elements, varying 

 in size and shape, intermixed with irregular light areas, which are 

 occupied by thin-walled parenchyma and in part by the calcareous 

 mineral matrix which has replaced the parenchymatous tissue. 

 The large diameter of the primary xylem elements shown in 

 PI. VI. (fig. 7) is at once apparent on comparing them with the 

 tracheids of the secondary wood, which forms the periphery of the 

 section. These wide constituents of the stele are tracheids of a 

 peculiar character, with their walls covered with numerous bordered 



1 Cf. Heterangium tiliaeoides, Williamson and Scott (95), PI. xxix. fig. 34, and 

 Poroxylon [Eenault (79), PI. lxxiv. fig. 8]. 



2 Seward (97). 



3 Williamson and Scott (95), Pis. xviii., xxi., xxn., etc. 



4 Scott (99), Pis. vi., xi., etc. 



5 Eenault (93), PI. lxviii. 



