Notes. 
615 
genera Lyginodendron and Heterangium approach most nearly to the 
Osmundaceae and Gleicheniaceae respectively ; in Megaloxylon, on 
the other hand, the structure of the primary xylem affords evidence 
that the Lygodium type of stem was also represented in the Cycad- 
fern alliance, which played so prominent a part in Palaeozoic 
vegetation. 
A. C. SEWARD, Cambridge. 
ON THE PRIMARY WOOD OP CERTAIN ARAUCARI- 
OXYLONS. — The genus Araucarioxylon of Kraus ( Araucarites , 
Goepp., Dadoxylon , Endl.) is used to include those fossil Gymno- 
spermous woods which have approximately the structure of the recent 
Araucaria or Dammar a. The characters of the genus as given 
by Kraus are as follows : c Lignum stratis concentricis distinctis vel 
obsoletis ; cellulis prosenchymatosis porosis ; poris magnis rotundis, 
rarius uniserialibus contiguis, creberrime pluriserialibus spiraliter 
dispositis compressione mutua hexagonis ; cellulis ductibusque resini- 
feris nullis ; radiis medullaribus uni- rarius pluriseriatis V 
The genus is admittedly an artificial and provisional one. From 
the investigations of Grand’Eury and Renault we know that many, 
though not necessarily all of the Palaeozoic Araucarioxylons were 
identical with the wood of the Cordaiteae, that remarkable extinct 
Order of Gymnosperms which those observers have revealed to us. 
Other specimens, and especially those of Mesozoic age, no doubt 
belonged to true Coniferae ; in fact the secondary wood, by itself, 
is of little value as a guide to affinities. Where other tissues, such as 
the pith and primary xylem, are also preserved, the case is a good deal 
more favourable, for we then have the anatomical ground-plan of the 
organ before us. The study of the primary tissues will no doubt lead 
in the future, as it has done in the past, to the gradual breaking up of 
these artificial genera into more natural groups. 
In the Cordaiteae and in the more typical Araucarioxylons generally, 
the primary wood of the stem, where it has been investigated, has 
proved to be purely centrifugal in development, the first-formed spiral 
tracheides lying at the inner edge of the wood, adjacent to the pith 1 2 . 
1 In Schimper, Paleontologie Veg&ale, vol. ii, p. 380, 1870. 
2 I leave out of account, for the moment, such stems as those of Protopitys or 
Lyginodendron , which were at one time included under Araucarioxylon, but have 
long since been separated. 
