XLV] WALCHIA 279 



case of specimens too- small to show the characteristic branching- 

 habit, has led to confusion between the two genera. It is often 

 very difficult to draw a definite line between Walchia and Ulbnannia, 

 and in the absence of sporophylls the genus Gomphostrobus may be 

 easily confused with species of Walchia. 



Foliage-shoots characterised by a pinnate arrangement of the 

 ultimate branches (fig. 745) attached at right-angles or obliquely 

 to an axis of higher order. Leaves spirally disposed, crowded and 

 imbricate, short and ovate or linear and spreading, usually tetra- 

 gonal and more or less falcate and decurrent. The dimorphism of 

 branches and differences due to age or position on the tree render 

 a satisfactory delimitation of species almost impossible though 

 a few fairly well defined types can be recognised with reasonable 

 certainty. As Bergeron 1 says, in the absence of strobili the 

 separation of species represented only by sterile shoots is hardly 

 possible. Further reference is made to the features exhibited by 

 reproductive shoots in the appended account of a few selected 

 types. Information with regard to the anatomical characters of 

 Walchia is very scanty and is based on evidence afforded by the 

 association of foliage-shoots and petrified wood or on inferences 

 drawn from unconvincing considerations. Among specimens 

 which may belong to this genus one of the more interesting is that 

 on which Mougeot 2 founded the species Araucarites valdajolensis. 

 The type-specimen, from the Permian of Val d'Ajol in the Vosges, 

 has been refigured and critically discussed by Fliche 3 though no 

 complete investigation of its structure has been made. The 

 cylindrical piece of stem, 9 cm. in diameter, has a large pith and a 

 broad zone of secondary wood composed of tracheids, with two 

 rows of alternate bordered polygonal pits, and narrow medullary 

 rays. It seems clear from Mougeot's brief account and from the 

 description of other specimens by Fliche that the anatomical 

 features are Araucarian though we have no information as to 

 the structure of the inner edge of the xylem, a regton of special 

 importance as regards comparison with other types possessing 

 a similar Araucarian pitting on the tracheids. The surface of 

 Mougeot's specimen is characterised by numerous spirally dis- 

 posed, elliptical projections 5 7 mm. long and 3 4 mm. wide 



1 Bergeron (84). 2 Mougeot (52) A. p. 27, PI. iv. 3 Fliche (03). 



