OF LOWER CJREFASAND PLANTS. 117 



vertical resin-canal*, forming tangential bands in the autumn 

 wood, are a very conspicuous feature of this plant. Large hori- 

 zontal canals can also be seen in transverse section running in 

 the medullary rays across more than one growth-ring. 



Medullary rays are uniseriate and multiseriate, the latter 

 containing resin-canals. The uniseriate rays are broad and con- 

 spicuous, from 1 to 6 tracheids distant. In radial extension 

 many of the elements are short, only 1| or 2 tracheid widths 

 in extent. In radial section the existence of ray-tracheids is 

 very clear. 



DETAILS OF ELEMENTS. The spring tracheids (PI. VIII, fig. 2) 

 are generally crushed, though a few patches remain uncrushed. 

 The elements are large, squarish, and, where uncrushed, fitting 

 into each other with but little rounding of the corners. They 

 measure as much as 50 x 65 ^/, 40 x 50 yu, and some even up to 

 90 fj. in diameter. Even in the first-formed spring wood the walls 

 are thick, being as much as 4 p. in the largest spring elements 

 adjacent to the last-formed autumn wood. The autumn tracheids 

 have extremely thickened walls, often leaving only a small 

 round pore or slit-like lumen (text-fig. 28) ; these walls may be 

 as much as 12 p thick. The radial walls of the tracheids 

 are pierced by large bordered pits, lying in one row, when 

 the round border approximately fills the width of the trachoid- 

 wall (as in PL IX, iigs. 1 & 2, a). Sometimes in such a tracheid 

 the single pits are intermingled with pairs of pits closely crushed 

 together and within the same "Sanio's rim'' (as in PI. IX, fig. 1,6), 

 which might be described as " twin pits." On the other hand, 

 a large number of the tracheids have pits in adjacent pairs 

 (as in PI. IX, c, aud text-fig. 29). 



In the autumn wood some of the walls are seen in transverse 

 section to be tangentially pitted, but the great thickness of the 

 walls somewhat distorts the pits. In all the bordered pits 

 observed on tracheid-walls, the pores are round (PI. IX, fig. 1). 

 Some close, very faint striations are noticeable in the longitu- 

 dinal views of the tracheids ; these may possibly be based upon 

 some sort of tertiary thickening in the walls, but it is not clear 

 that it is not due solely to the arrangement of the mineral 

 matrix. 



Wood-parenchyma appears to be absent from the general 

 texture of the wood, but groups of large wood-parenchyma cells 



