214 CONIFEEALBS [CH. 



medullary-ray cells affords an important distinguishing feature. 

 In Cedroxylon they are characterised by the occurrence of pits on 

 all the walls as in Abies, Tsuga, Cedrus, Larix, Picea, Pseudolarix, 

 while in wood of the Cupressinoxylon type there is no Abietineous 

 pitting but only pits on the radial walls. Another distinguishing 

 feature, mentioned by Lignier, — whether important or not is open 

 to question — is based on the greater number of medullary rays 

 per square millimetre in Cupressinoxylon. 



The characters of Cedroxylon may be briefly summarised as 

 follows : — Annual rings well marked ; bordered pits on the radial 

 walls of the tracheids usually circular and separate and if in more 

 than one row, opposite, but in some species the Araucarian type of 

 pitting also occurs (fig. 723), the pits being contiguous and alternate 

 or sometimes arranged in stellate clusters. Xylem-parenchyma 

 typically confined to the end of an annual ring, but sometimes 

 absent; medullary rays generally uniseriate and composed ex- 

 clusively of parenchyma though horizontal tracheids may occur ; 

 pits on all the walls of medullary-ray cells as in the Abietineae; 

 on the radial walls there may be 1 — 6 apparently simple circular 

 pits in the field. There are no resin-canals except as the result 

 of injury. 



Cedroxylon transiens Gothan. 



This species from Upper Jurassic rocks in Spitzbergen^ and 

 from Lower Cretaceous beds in King Charles Land^ illustrates the 

 admixture of opposite, separate, and contiguous, alternate, pits 

 in the same wood (fig. 723, A, B) ; stellate groups also occur 

 (fig. 723, A), an arrangement occasionally seen in some recent Pines, 

 e.g., Finns MerJcusii^. The Araucarioid type of pitting is charac- 

 teristic of the spring- wood where it is associated with the more usual 

 opposite and separate arrangement. Smaller separate pits occur on 

 the tangential walls of some of the tracheids. Resin-canals are 

 absent, though a solitary example is recorded by Gothan. The 

 medullary rays have several small pits in the field, also pits on the 

 tangential and horizontal walls ; the xylem-parenchyma is confined 

 to the end of the year's wood ; the cross-walls are pitted (fig. 723, B). 



1 Gothan (10) p. 38; PI. vi. figs. 11—13. 



= Ibid. (072) p 26. figs. 14, 15 ; PI. i. fig. 1. 



^ Groom and Rushton (13) PI. xxv. figs. 47, 48. 



