Comparative Anatomy of the Casuarineae . 239 
an oblique series of tracheides stretching from the xylem to 
the palisade-tissue. 
The tracheides of this transfusion-tissue appear in all cases 
to be a modification of the parenchymatous-tissue of the 
cortex ; as proof of this it was noticed in one section that, in 
a mass of similarly-shaped, irregular elements, some were 
developed as tracheides, with thick and pitted walls, while 
others, scattered amongst them, were ordinary thin-walled 
parenchyma-cells; and moreover, in one or two places, half 
of such an element was thick-walled and pitted, and the other 
half thin-walled and unpitted . 
The pits are always simple, but of various sizes and shapes : 
often small and oval in outline, at other times narrow and 
slit-like, and sometimes stretching right across the cell, so as 
at first to give it the appearance of having spiral thickenings. 
In one isolated instance, a tracheide was observed far out 
amongst the palisade-cells. 
Loew 1 , in his description of these elements, calls them 
‘ thickened cells of the leaf-parenchyma,’ comparing them with 
reticulate parenchyma-cells in the petiole of Cycas revoluta , 
and in the parenchyma of the leaves of Sanseviera guineensis 
and others. He is quite uncertain as to whether they belong 
to the vascular bundle or to the surrounding parenchyma. 
Lecomte 2 also thus shortly mentions the occurrence of 
pitted, thick-walled elements connected with the tracheides 
of the cortical bundle : — ‘ Ces faisceaux dans un certain 
nombre d’especes, mais surtout dans le C. qnadrivcilvis , Labill, 
se ramifient a droite et a gauche, et ces ramifications, d’ailleurs 
tres courtes, vont se terminer de chaque cote dans le paren- 
chyma Les trachees viennent appuyer leurs extremites contre 
le cloison de cellules un peu plus grandes que les autres, a 
membrane un peu epaissie, et munie de ponctuations simples.’ 
Cluster-crystals of calcium oxalate frequently occur in 
some of the palisade-cells as well as in those of the inner 
cortical tissue. 
1 Loc. cit., p. 13. 
2 Loc. cit., p. 313. 
