294 
PROFESSOR W. C. WILLIAMSON ON THE ORGANISATION 
from Halifax, I soon found that the cortical tissues of the two forms had been 
identical. 
At the same time, the Halifax specimens had peculiarities of their own which 
seemed difficult of explanation. The forms most generally met with at Oldham were 
of the type represented in my earlier memoir by the two figures, Plate 5, figs. 23 and 
26, in which six large exogenously developed vascular wedges radiated from what 
appeared to be a central vascular axis. At that time I was unable to discover any 
cellular tissue in that axis ; I have since obtained three or four examples like those 
just referred to, from Halifax, one of which is represented in Plate 23, fig. 20, of the 
present memoir. But most of the Halifax specimens are like those seen on Plate 24, 
figs. 22 and 27. 
That fig. 20 is the Kaloxylon Ilookeri of my former memoir is unquestionable. In 
that memoir I called attention to a special development of cells at the free extremity 
of each of the six radiating vascular wedges {Joe. cit., p. 15). The cells occupying the 
peripheral ends of the six primary medullary rays separating the six radiating vascular 
wedges were enclosed within a wavy line round, and at a little distance from, the end of 
each of those wedges, where “ they enclose a small semi-lunar area ( g) co-extensive with 
the diameter of the wedge, and which is occupied by a distinct form of cellular tissue. 
I shall shortly give my reasons for believing that this latter tissue is a quasi-cambial 
meristem layer, which is concerned in the formation of the newest exogenous vascular 
growth.” 
More extended investigations into the structure of this curious plant lead me to 
the conclusion that the above extract embodies a truth, but not all the truth. 
Plate 23, fig. 20, represents an excellent example of this stem from Halifax. As in the 
corresponding Oldham examples, the central axis is a bundle of vessels apparently 
unmixed with any cellular tissue. The radiating wedges, c (which are here five, not 
six, in number), and their five intervening primary medullary rays, g, do not differ 
from those of the Oldham forms. But the semi-lunar areas of the Oldham specimens 
represented in fig. 15, g, of the memoir quoted in the above paragraph are clearly 
seen in fig. 20 , k, k ', of this memoir, to be the true phloem-masses of the several 
radiating wedges, and not a quasi-cambium as previously surmised; but which must, 
when the plant was living, have had a true cambium separating the inner border of 
each phloem from the periphery of the xylem. Plate 23, fig. 21 , represents the phloem 
of the radial bundle, k, of fig. 20, enlarged 62 diameters ; at p we have the long- 
narrow cells of the innermost margin of the cortex pursuing their undulating course, 
sweeping outwards opposite the ends of the xylem-wedges to make room for the 
phloem-masses, k, k', and curving inwards when crossing the outer ends of the primary 
medullary rays, g, g, as at g , g'. There can be no doubt, therefore, that the Kaloxylon 
Hookeri was a true exogen, having a perfect cambium, which developed both xylem 
and phloem, but the traces of which cambium are but very imperfectly, if at all, 
preserved. 
