OP LOWER GREENSAND PLA.NTS. 165 



TYPE. Twig about 2'4 cm. in diameter ; block, and some 

 sections cut from it in 1912 in the Sedgwick Museum, Cam- 

 bridge ; also sections V. 13197 a to V. 13197 c, British Museum 

 (Nat. Hist.). 



The specimen on which this " species " is founded is a de- 

 corticated twig, now about 2'4 cm. in diameter, but which could 

 not have been less than 3'5 cm. when alive. It is stained with 

 the reddish-brown colour which is characteristic of the Potton 

 material, and the preservation of the tissues is so blurred that 

 they cannot be satisfactorily described. A second, still more 

 poorly preserved, specimen is here provisionally associated 

 with it. 



DESCRIPTION. -PiiJi is preserved and measures 1 mm. in 

 diameter ; it is roughly circular, with irregular bays of primary 

 wood projecting into it. The secondary wood is close-grained 

 and regular, and has well-marked growth-rings up to 3 mm. in 

 extent. The elements of the spring wood are all considerably 

 thickened. The zone of autumn wood is broad, the elements 

 rather rounded and very thick-walled, but not excessively com- 

 pressed radially. 



Throughout the wood the elements are considerably rounded 

 off, and alternate to fit into each other, but even so leave 

 considerable intercellular spaces; they meat lire up to about 

 30-40 ft in diameter. The pitting of the tracheids is 

 very obscure, but seems to consist of round bordered pits in 

 one row, 



Retin-canab are absent, resin-containing (?) wood-parenchyma 

 seems to be present in small quantities, and in the summer wood 

 are a good many parenchyma-cells with horizontal cross-walls 

 at short intervals. 



Medullary rays are fairly conspicuous, 4-15 tracheids distant, 

 the cells as wide or slightly less than the adjacent tracheids. 

 The rays are all uniseriate and principally from one to a dozen 

 cells high. There seems to be no differentiation into ray- 

 tracheids or specialised cells. The walls of the medullary ray- 

 cells are better preserved than the rest of the tissues and show 

 true "abietinean pitting." A false appearance, somewhat 

 similar, is present in most of the tracheid-walls, but in the 

 medullary rays the true thickening and pitting of the walls can 



