206 DESCRIPTIVE CATALOGUE 



section many of the ray-cells are blocked with black contents. 

 The rays are principally 2-10 cells in height, 2 and 3 being 

 the commonest number. 



The secondary tracheids vary, the larger first-formed elements 

 averaging from about 25 x 30 to 30 x 40 /x. In proportion to 

 their size, the cell-walls even of the first-formed elements arc 

 rather thick, measuring as much as 4-6 /z. The compressed 

 autumn elements often have a wall so thickened as almost to 

 obliterate the lumen, which is a narrow slit-like space. The 

 individual elements in the wood are considerably rounded off, 

 and adjacent elements lie on alternating tangents so as to fit 

 into each other ; but even so there are noticeably large inter- 

 cellular spaces between the corners of many of the tracheids. 

 The radial walls are pitted with round bordered pits (PI. XIX, 

 fig. 3, and text-fig. 59). The pits nearly all lie in a single 

 row, isolated by at least a distance equal to their own border. 

 The diameter of the border is about equal to g the diameter of 

 the trachcid-wall in which it lies. In several cases the border 

 appears to be double, with an inner and an outer circular zone 

 but this may be petrifact, as the tissues are rather dia- 

 phanously preserved. Sanio's rims are clearly to be seen in 

 many cases, and there are in addition exceedingly fine reticu- 

 lations over the surface of the tracheids (text-fig. 59, n.). Under 

 the microscope these are very different from the fine cracks 

 which are often seen in semi-decomposing walls and are highly 

 suggestive of true, delicate, tertiary spirals, such as are seen, 

 more coarsely developed, in living Taxacca'. 



Resin-containing ayyfem-jHtr^nofypmd cells at first sight appear 

 to be frequent, but after careful examination I have not been able 

 to find any cells which satisfy me that they are true parenchyma. 

 The blackened contents, which are so deceptive in transverse 

 section, are due apparently to mineral granules. 



Medullary rays are all uniseriate, and the cells composing 

 them are from one half up to the same tangential width as the 

 adjacent tracheids. In transverse section the end-walls are at 

 a low angle or slightly curved. In radial section the walls arc 

 still more curved, and some of the elements are rather irregular 

 or slightly spindle-shaped. The walls appear (as preserved 

 in this specimen) to be very delicately thickened, and so it 

 is riot easy to determine whether they have the so-called 



