242 Boodle and W or s dell. — On the 
appearance of fibrous cells than of fibrous tracheides, for 
they were full of contents and had quite a thin wall ; but 
these were fibrous tracheides not yet fully mature, which 
retained their protoplasmic contents till their growth was 
complete. When a fibrous tracheide borders on a medullary 
ray-cell, the common wall has a half-bordered pit. 
The vessels occur scattered throughout the wood, not ar- 
ranged in any definite radial rows. In the primary wood 
they have usually a much smaller cavity, sometimes quite 
narrow, which increases in diameter as one passes further out. 
On the whole, the vessels in Cctsuarina have a comparatively 
narrow cavity ; in one species they seemed rather larger than 
in any of the other * ones examined. The vessels are usually 
surrounded by narrow parenchymatous cells ; sometimes they 
border directly on fibrous tracheides ; occasionally, two vessels 
are in contact with one another or with ordinary tracheides. 
The vessels occur scattered amongst the fibrous tracheides, 
and they may often be seen disturbing the course of a me- 
dullary ray and causing it to bend some considerable way out 
of its path. 
Annual rings are not distinguishable, and the vessels are 
uniformly distributed throughout the wood. 
The most striking feature in the wood of Casuarina is the 
concentric bands of xylem-parenchyma connecting the me- 
dullary rays. These were noticed by Goeppert 1 , and called 
by him 4 concentric medullary rays.’ They were the c false 
annual rings’ of other authors. By means of these bands 
the wood is abundantly furnished with parenchyma. Sanio 2 
gives this tissue the name of * metatracheal parenchyma,’ to 
distinguish it from that immediately surrounding the vessels, 
which he terms c paratracheal.’ The concentric bands are not 
quite regular in their course, being often interrupted by the 
vessels, and also here and there fusing above and below with 
one another. They contain starch, &c. (Fig. 12 pin). 
If a section is made through that part of the stem where 
1 Loc, cit. 
2 Loc. cit., 1863, p. 389. 
