OF LOWER GREEXSAND PLANTS. 225 



small-celled, the elements being considerably rounded off and 

 lying on alternate tangents so as to fit into each other, liesin- 

 parenchyma is scattered all through the wood. Resin-canals are 

 entirely absent. 



The medullary rays are numerous, entirely uniseriate, about 

 1-8, chiefly 2-4, tracheids distant. Vertically the rays are low, 

 from 1-10 cells in height, principally 2-4 cells high. The cells 

 of the rays are all of one kind. 



DETAILS OF ELEMENTS. The great majority of the tracJieids are 

 of the size and character of the spring elements, and average 

 1 5 x 20 ju to 20 X 28 /* in diameter. Even in the spring wood the 

 walls are rather thick, and are so much rounded off at the corners 

 as often to be true circles, and in the majority of cases, therefore, 

 there are six small intercellular spaces round each tracheid sepa- 

 rating it from its neighbours. In transverse section bordered pits 

 are frequently to be seen on the radial walls, and in the autumn 

 wood also in the tangential walls. The bordered pits are in one 

 row in the radial walls, arid are nearly circular, but are a little 

 flattened top and bottom where they are adjacent to their 

 neighbours, and lie in close rows (PI. XXI, fig. 3 ; text- 

 fig. 04, t.). These groups or chains of pits number from 3 to 10 

 or more, and lie, as a rule, in the thicker parts of the tracheids, 

 which are themselves rather peculiar, alternately increasing and 

 decreasing in thickness (in text-fig. G4 at n. is a thin part of a 

 tracheid, and in the thicker part above and below it are chains 

 of pits). In the narrower zones of the tracheid-length the walls 

 appear to be without pits. Isolated pits are very uncommon in 

 this wood, practically all the elements having chains of adjacent 

 pits such as are figured. *' Rims of Sanio " are consequently not 

 visible, and the wood would therefore be put in the Araucarineae 

 by some authors. Wood-parencliyma containing resin is scattered 

 through the xylem, and the cross-walls are horizontal, with a 

 very slight constriction of the cell-lumen, llesin-canals and 

 specialised resin-tracheids seem to be entirely absent. 



In transverse section of the medullary rays the tangential 

 diameter of the ray-cells equals or is less than that of the 

 adjacent tracheids. In radial extension the ray equals about 

 2-6 tracheids. The vertical height of the individual ray-cells 

 may be as great as, or once and a half as great as, the width of 

 the adjacent tracheids (text-fig. 04, t.). The pits in the radial 



