86 DESCRIPTIVE CATALOGUE 



axis of the cells. But most of the elements which at the first 

 glance appear to be parenchyma-cells are tracheids in which 

 a very fine u spindle " of resin lies across the lumen (see text- 

 fig. 22, rs.). There are also imperfect spindles in many of the 

 tracheids adjacent to the rays. The wood parenchyma-cells 

 nearly all contain resinous remains. A small number of paren- 

 chyma-cells are also associated with the resin- canals. 



Resin-canals are normally present in the second and all sub- 

 sequent rings. They are very beautifully preserved, and show 

 their simple structure admirably. The majority of them are 

 very small, as can be seen in text-fig. 17, but a number of them 

 are rather larger and more irregular. The typical resin-canal, 

 however, has only 4 or 6 epithelial cells, and sometimes these are 

 arranged with extraordinary symmetry (see rc., text-fig. 17). 

 In other cases the epithelium-cell projects curiously into the 

 cavity of the canal, as rcb., text-fig. 18. Some of the canals, 

 not yet completely formed, show very beautifully their mode of 

 origin and development (see red., text-fig. 18). 



The walls of the epithelium are all thickened, and in some of 

 the longitudinal sections their pitting can be well seen (text- 

 fig. 19). The epithelium -cells appear to have sometimes straight 

 and sometimes pointed ends ; the xylem-parenchyma cells just 

 outside them in some cases have generally rectangular end- walls. 

 Most of the canals lie in tangential bands, as is seen in the 

 figures, but a few are isolated. They generally lie just about 

 the middle of the autumn wood. I have not observed any tyloses 

 in the canals. 



Medullary rays. In transverse section the medullary ray- 

 cells, particularly in the first five or six wood-rings, may have 

 a tangential diameter as great or even greater than the adjacent 

 tracheids ; many rays, however, have cells a good deal narrower 

 than the adjacent tracheids. The majority of the ray-cells equal 

 2 or 3, but may equal 5 or 6, tracheids in radial extent. The 

 end-walls slope slightly, and even in the transverse section ; 

 with the high power the thickening and " abietinean " pitting 

 of these walls can be made out (see text-fig. 17, mw.} in many 

 places* In examining these sections deceptive appearances, due 

 to mineral depositions round the walls, must be avoided. The 

 well-marked " abietinean pitting " of the ray-cells may also be 

 seen in some of the radial sections (text-lig. 20), where the 



