Young Plant of Macrozamia Fraseri. 577 
apart from the leaf-traces has not been determined. The cambium of these 
‘ anastomoses ’ becomes continuous with the ‘ anomalous 5 cambium, and 
thus a complete cambial ring is eventually established, appertaining to 
a vascular cylinder of extreme irregularity lying outside the normal vascular 
ring (Plate XXII, Fig. III). 
(7) Tangential extension in the anomalous ring . The second ring, 
once well established, is seen to become affected by the phenomenon of 
tangential stretching already described. At the extreme base of the stem 
we have thus the following structure (Plate XXII, P'ig. Ill) : 
A pith, surrounded by a vascular cylinder composed of radially 
arranged wood, tangentially running wood, tangentially elongated cambium, 
tangential phloem, radial phloem. Outside this, a second vascular ring 
which, though more irregular and less complete than the normal ring, is 
composed of the same tissues arranged in the same order. 
(8) The cotyledonary node. At the cotyledonary node the complica- 
tion becomes extreme. Seen both in longitudinal and transverse section, 
the xylem tracheides pursue courses of extraordinary irregularity, often 
doubling back on their original path. In this region the two vascular 
cylinders become very closely approximated, and it is sometimes difficult 
to say to which cylinder certain elements belong ; there are indications 
that a third anomalous ring is in process of formation, but the whole 
structure is too irregular to admit of any very satisfactory interpretation 
(Plate XXII, Fig. IV). 
(9) The root . The extremely long tap-root is usually diarch in 
structure, and no increase in the number of poles, as the apex is approached, 
such as has been described for seedlings by Hill and de Fraine, 1 has ever 
been observed. In one case, a triarch root, reducing to diarch, occurred. 
The structure is of the normal gymnospermous type ; the many-layered 
pericycle consists of cells tangentially elongated and flattened, many of 
these having lignified walls. In no case has any anomalous thickening 
been detected (cf. Gregg 2 ). 
As the hypocotyledonary region is approached there is evidence that 
there is stretching, and finally division, of the cells of the usually uniseriate 
medullary rays, until these rays are 4-5 cells wide. 
(10) The swollen hypocotyl. The swelling characteristic of the upper 
hypocotyledonary portion of the axis is due to an enormous increase, as 
compared with the root region, in the parenchyma present. Pith and 
pericycle are both considerably enlarged by the stretching and division of 
their cells ; the xylem is invaded by parenchyma ; the medullary rays 
increase in size, while each radial row of wood elements becomes broken up 
into several groups by the intrusion of non-lignified tissue (Text-fig. 7). 
1 Hill and de Fraine: loc. cit. 
2 Gregg : Anomalous Thickening in the Roots of Cycas siamensis. Ann. Bot., vol. i, 1887. 
