PITYEAE 515 



length ; at the top, the wood still had a diameter of 

 1 \ feet. 



The pith and wood are the only parts preserved in 

 any of the species, as at present known. The wood, 

 except for the greater width of the principal medullary 

 rays, is of the Araucarian type, and thus, as we shall 

 see, agrees with that of the Cordaiteae (cf. Fig. 190, 

 p. 528); the secondary tracheides have rhultiseriate 

 bordered pits, confined for the most part, to their 

 radial walls. 



The point of chief interest is the presence, in 

 all three species, of a number of small strands of 

 primary wood, disposed around the pith. 1 This 

 structure is best shown in Pitys antiqua, the Lennel 

 Braes tree, from which the illustration in Fig. 186 

 is taken. The imperfectly discoid pith is large, some- 

 times as much as 2 inches across ; in a specimen 

 where the pith measured only 22 mm. in diameter, 

 the number of xylem -strands round the pith was 

 between forty and fifty. The diameter of each 

 xylem -strand is small, averaging about '25 mm.; 

 most of the strands are embedded in the pith at 

 some little distance from the inner edge of the 

 woody zone (Fig. 186), with whjch they only come 

 into contact when about to make their exit as leaf- 

 traces. Where a xylem-strand passes out into the zone 

 of secondary wood, its place is taken by a reparatory 

 strand lying behind it, deep in the pith. The outgoing 

 strand shows some sign of division into two, but the 

 two halves appear to reunite further out in its course. 



1 Scott, " Primary Structure of certain Palaeozoic Stems," etc., Trans. 

 Roy. Soc. Edinburgh, vol. xl. Part ii. 1 902. 



34 



