OF LOWER GREENSANI) PLANTS. 205 



per tracheid-field of 2-4 pits with large definite borders. 

 Connecting rays which lie near to each other are short tracheids, 

 sometimes exceedingly irregular in shape, and with small 

 circular bordered pits. 



Species founded on a twig which cannot have been less than 

 4 cm. in diameter when alive. 



HORIZON. Lower Greensand. 



LOCALITY. Woburn Sands, Bedfordshire. 



TYPE. Twig, no. V. 5459 and V. 5459 a-d, slides cut from 

 it in 1912 ; British Museum (Nat. Hist.). 



DESCRIPTION. The specimen is a length (8 cm.) of decorticated 

 woody stem at present about 2-5 cm. in diameter, but of which 

 the size must have been greater, as the pith is preserved very 

 much to one side, making the diameter when living and corti- 

 cated probably about 4 cm. Externally the woody texture is 

 weathered out and the surface is considerably teredo-bored. 

 It is well petrified, with a close hard texture, dark centrally, 

 and whitish round the edges. 



TOPOGRAPHY OF STEM. The pith and primary wood, to the 

 extent of about 1 mm,., are entirely disintegrated. Secondary 

 wood is formed of regular series of close-grained elements, with 

 well-marked growth-rings, the larger of which measure about 

 2 ram. in radial extent and are composed of a variable number 

 of tracheids up to 90 in radial sequence. The zone of com- 

 pressed autumn tracheids is narrow, averaging from 5-10 

 elements, which have very thick Avails. 



lie sin-canals, both normal and traumatic, are absent, liesin- 

 containiny xylem-partnchyma is very sparsely developed, even 

 if present, a point about Avhich I am in some doubt, oAving to 

 the difficulty of determining whether end-walls are present in 

 the cells in the radial section which appear to be resin-con- 

 taining. The numerous dark cells in the transverse section 

 are due to petrit'act*. 



DETAILS OF ELEMENTS. Medullary rays are fairly conspicuous, 

 averaging 2 to 10 tracheids distant. They are all uniseriate, 

 and in tangential section the cells seem all alike. Some of the 

 rays appear very close together and arc connected by A r ery short 

 tracheids, which almost merge into ray-tracheids. In tangential 



* Set 1 Slopes, 1012, ibotnoL'j, p. 0-1, fur the first u?e of this word. 



