bo 
Or 
FEB. 1909. | BOTANICAL SOCIETY OF EDINBURGH 
NoTE ON THE SEPTA IN Root VESSELS OF BROMELIACE. 
By Rev. JAmMEs WarTersTON, B.D., B.Sc. (Plate IT.) 
In cutting transverse sections of the hypogeal roots of 
many of the Bromeliacez one discovers frequently lignitied 
bars stretching across the lumina of the vasa. These are 
thickened portions of the terminations of the vascular 
elements. As these septa—for such they are till the 
cellulose membrane between the bars has broken down— 
generally run obliquely to the longitudinal axis of the root, 
one seldom finds them complete in a section of normal 
thickness. By taking sections a little thicker than usual 
one can note the nature of the pattern on the septum. 
Often this simply reproduces the thickening on the walls of 
the vasa. A common type, fig. 3, shows a series of parallel 
bars between which the original membrane has disappeared. 
Thus the lumen of the vas is at intervals crossed by a series 
of oblique gratings. Sometimes lignification goes further. 
The bars may be interconnected, and a somewhat reticulated 
septum results, tig. 4. Possibly owing to the strain being 
less, the original membrane may in such cases be preserved 
intact. Its presence can be demonstrated by staining with 
a suitable reagent. 
Recently, in almost perfectly transverse sections from 
roots of Pwya (three spp.), characteristic septa were noted. 
Their thickening does not copy that on the walls of the vas. 
It is broad and stout, with few bars on each septum. The 
original membrane may persist, fig. 1, or may be ruptured, 
figs. 2, 5. This often takes place irregularly, but in one 
case (P. chilensis) it is very definite. A septum of this sort 
must exercise a particular, regulative effect on the passage 
of any fluid through the vas. 
Doubtless also, when every trace of the cellulose mem- 
brane has gone, the struts of the septum will still be of 
considerable mechanical importance for the plant. In 
almost any root that would be the case. But it is an 
arrangement of special value for the Bromeliads. In this 
group the vasa are arranged in a peripheral zone round 
the thickened pith. Proximally they are embedded, it may 
be for fully two-thirds of their circumference, in a mass 
