XXXI V] ANTARCTICOXYLON 299 



due to the partial destruction of the secondary tracheids, but in 

 other places crushed parenchymatous tissue occurs which may 

 be a traumatic phenomenon or possibly comparable with Nord- 

 linger's 'medullary spots 1 ' formed by local hypertrophy of 

 medullary tissue. Although the structure of the leaf -traces cannot 

 be definitely determined, it would seem that each trace passed 

 into the perimedullary region as a single bundle of relatively 

 large size composed of spiral and scalariform tracheids narrower 

 than the secondary elements. The traces during their outward 

 course were accompanied by some parenchymatous tissue con- 

 tinuous with that in the pith, and the inner spiral tracheids of 

 the trace were connected with isodiametric reticulate elements. 

 The dimensions of the leaf-traces point to leaves of fairly large 

 size. 



In the structure of the secondary wood Antarcticoxylon agrees 

 on the whole with an Araucarian stem : the broad zone of xylem 

 composed of spiral and scalariform tracheids at the edge of the 

 pith is a feature common to Mesoxylon, Cordaites, and Araucaria. 

 There is no evidence of the occurrence of double leaf-traces such 

 as characterise certain Cordaitalean genera and some existing 

 members of the Araucarineae. In the single nature of the leaf- 

 traces the Antarctic stem resembles Mesopitys Tchihatcheffi also 

 in the presence of rings of growth 2 , but in Antarcticoxylon the 

 preservation of the primary xylem is too imperfect to admit 

 of any satisfactory comparison as regards this important tissue 

 with other types. 



The precise age of the Beacon sandstone has not been deter- 

 mined, but the probability is that the upper beds from which the 

 boulder containing Antarcticoxylon was derived are not older than 

 the Rhaetic period. The chief interest of this imperfectly pre- 

 served stem with undoubted Araucarian affinities is its occurrence 

 in the rocks of Antarctica in association with other remains of 

 comparatively large stems. 



1 De Bary (84) A. p. 492; Grossenbacher (15). 



2 See Scott, Nature, August 26, 1915. 



