OF LOWER GREENSAXI) PLANTS. 2,39 



scattered through the pith, are larger more irregular cells, up to 

 100 p in diameter, which are generally devoid of contents. There 

 are also roundish stone-cells with excessively thickened walls. 

 In longitudinal section the arrangement of these is peculiar, as 

 is shown in text-fig. 67, s. & 1. ; they form longitudinal chains, 

 one of the large empty cells alternating with two or three of the 

 stone-cells. These chains run for long distances vertically through 

 the pith, where they form a noticeable feature in longitudinal 

 sections (see slide V. 2117^). 



The wood round the pith forms bundles of primary xylera 

 which is apparently all centrifugal. The quantity of the proto- 

 xylem-eleraents is large, and in the second specimen, where it 

 is beautifully preserved, there are 8 or 9 spiral and narrow 

 finely scalariform elements lying on one radius (text-fig. 69, ^>#.). 

 In the secondary wood the tracheids increase in size as the wood 

 gets older. In the outer rings the average size of the spring 

 wood is 40 x 30 p to 55 x 45 //. The narrowest autumn tra- 

 cheids are about 10 to 12 jj, x 30 or 40 /i, with a wall 4-5 p 

 thick. 



The pits on the radial walls are principally in one row, 

 most of them being isolated from each other by a distance equal 

 to their own border. Most of the pits are small, the diameter 

 of the border being equal to about half that of the tracheid in 

 which it lies. In a few cases a second row of pits lies in the 

 radial wall (text-fig. 70). Pits are present in the tangential 

 walls of the autumn wood. 



Wood-parenchyma containing resin is scattered through the 

 wood. The transverse walls of these cell-rows slightly constrict 

 the lumen in the radial section (text-fig. 70, rp.}. In the tan- 

 gential section these walls are straight. The walls appear to be 

 somewhat thickened, but I have not detected special pitting in 

 them. 



Traumatic resin-canals only are present, and they show no 

 special feature ; they lie in irregular tangential rows (PI. XXII, 

 fig. 2). In regions cut apparently above or below the endings of 

 these canals large parenchymatous cells and enlarged cells of the 

 medullary rays are conspicuous. None of these elements show 

 any special pitting. 



In transverse section the medullary rays are very incon- 

 spicuous, the cells having a tangential diameter of only j to * 



