352 DR D. E SCOTT ON THE 



deceptive, and the spaces due simply to the contraction of the surrounding tissue. 

 Traced out into the wood, the rays soon assume the ordinary structure ; their tissue, 

 as seen in radial section, has the usual muriform character (see PL V. fig. 18). The 

 cells usually retain some remains of their contents, often in the form of definite granules. 

 Secondary rays appear between the principal ones, as best shown in specimens where 

 the wood attains some considerable thickness. 



Seen in tangential section (PL VI. fig. 19) the larger rays are found usually to reach a 

 width of four cells, sometimes five or even six, and are often of great height, seventy cells 

 or upwards in some cases. Among the large rays, however, much smaller ones occur, 

 only one cell thick, and of small height, sometimes reduced to a single cell. At one 

 or two places an isolated strand of xylem-parenchyma was observed, consisting of a 

 row of vertically elongated cells, at least three times as high as those of the rays. 

 This tissue is, however, extremely scanty, and in most sections is not shown. 



The tracheides are exquisitely preserved. Those at the inner edge of the secondary 

 wood are transitional between the reticulated and pitted forms ; the spirally arranged 

 reticulations are distinctly bordered (fig. 17). Further out in the wood, the spiral 

 arrangement becomes less marked, and the pits assume the characteristic hexagonal 

 form (fig. 18). They are ranged in four or five ranks, on the radial walls of the large 

 tracheides, and are usually in contact with one another throughout. Occasionally, how- 

 ever, especially near the ends of the tracheides, the pits are more scattered, as Witham 

 described them,* and may be even reduced to a single row, leaving the rest of the 

 wall bare. The border of each pit is, as a rule, perfectly preserved, enclosing a narrow 

 slit or pore, usually in an inclined position (fig. 18). A more perfect example of 

 typical ' Araucarioxylon 7 structure than that presented by this wood could not be 

 imagined. 



The tangential walls of the tracheides are, as a rule, without pits, but exceptions 

 occur, especially in the inner layers of the wood. A good example is shown in fig. 20, 

 where a number of pits (t.p.) are seen on the tangential wall of a tracheide. Where 

 they occur, they are less crowded than those on the radial walls, and do not cover the 

 whole surface. Tangential pits are of common occurrence in the wood of the Coniferse, 

 especially in the first-formed layers, and in the tracheides of the autumn wood.f 



We may sum up the chief anatomical characters presented by the stem of Pitys 

 antiqua as follows : — 



(1) The pith is large (22 mm. to 34 mm. or more in the specimens examined) and 

 consists of short-celled parenchyma, interrupted by extensive horizontal lacunae, prob- 

 ably due to shrinkage of tissue. 



(2) Around the periphery of the pith, and usually at some little distance from the 

 inner edge of the secondary wood, are a large number (40-50) of small primary xylem- 

 strands, which occasionally anastomose with one another. The central elements of each 

 strand are spiral tracheides, indicating a mesarch structure. 



* L.c, p. 38. t L.c, Strasburgkr, " Leitungsbahnen," Histologische Beitrage, iii. p. 9, 1891. 



