Slopes. — A New Araucarioxylon from New Zealand. 343 
wood : the distinction between the two regions of the same woody trunk 
depends on the fact that the core is silicified and the outer zones preserved 
in carbonates. The contrast between the two regions is very well marked 
when weak hydrochloric acid is poured on the cut surface : the inner zones 
are not affected at all by the acid, but stand out like a placid island in 
a surrounding sea of excited effervescence. It is noticeable that the inner 
zones of the wood of the carbonate region (that is, those which lie just out- 
side the part preserved in silica) are very poorly preserved, or are entirely 
eliminated. It looks as though the change in the petrifying medium had 
upset the preservative properties of the mineral. The outer zones of the 
wood, though in the carbonate matrix, are fairly well preserved. The 
mineralization of this specimen suggests a number of interesting problems 
concerning the mode of penetration of two different petrifying fluids, the 
possible priority of one and its replacement by the other, the time required 
for the preservation of the wood, &c. ; but this one specimen does no more 
than suggest, it does not solve the problems it raises. 
Topography of the Stem . : Pith. Owing to imperfect petrifaction, and 
also to a break in the centre of the stem, little of the pith remains. It is 
clear, however, that it was small (i. e. not more than 1 mm. in diameter), 
and that the cells composing it were rather large and irregular in outline. 
Growth rings are exceedingly well marked. The autumn wood cells 
are so thickened as almost to obliterate the cell lumen. The size of the 
rings varies from about 1 mm., consisting of about 36 cells, to small rings 
of about 10 cells in radial sequence. On an average the spring wood 
is about equal to the autumn wood in extent (see Photo 3), but owing to 
its markedly thinner walls it tends to be crushed in many parts of the 
specimen. 
Wood elements. The radial diameter of the tracheides varies from 
25 to 36 n on an average, the last cells of the autumn wood being much less 
than this (see Text-fig. i,a). Thickened ‘resin’ containing tracheides are 
noticeable on either side of the ray, and will be described below. The 
general build of the tracheides both of spring and autumn wood is indicated 
in Text-fig. 1 and Photos 3 and 4. But few pittings are to be seen in transverse 
section ; in longitudinal section the preservation is not very sharp, but 
a number of elements show the typical Araucarian pitting, as indicated in 
Text-fig. 2, t. In the majority of the elements which show pitting at all, 
the pits are biseriate, alternating, and mutually hexagonally compressed. 
Special tracheides contain tannin (see below). Wood parenchyma was not 
observed. 
Medullary rays. Simple, uniseriate rays are numerous throughout the 
wood. In radial extension they tally with 3-4 tracheides. The rays are 
principally 3 and 4 cells high, as judged from 133 counts in various regions 
of the sections. 
A a 2 
