575 
Young Plant of Macrozamia Fraseri . 
(3) The vascular cylinder. In the upper region of the stem described 
above, there is very little development of lignified tissue, the only xylem 
elements being differentiated in the leaf-traces. About i| cm. below the 
apex, the meristematic dome of tissue, pith, and peripheral ‘ growth zone * 
is replaced by a ring of collateral endarch bundles surrounding a pith. 
These bundles represent the stelar portion of the traces of older leaves. 
The transition from a meristematic ring of tissue, with an occasional 
lignified element in connexion with an entering leaf-trace, to a complete 
ring of endarch and secondarily thickened bundles, is a somewhat sudden 
one, and suggests that we are perhaps dealing with structures appertaining 
to two successive periods of developmental activity, separated by a quiescent 
period. 
There is thus established a ring of collateral vascular strands, the ring 
thus constituted being completed by the development of a small amount of 
interfascicular xylem and phloem. 
The wood consists of irregular rows of xylem elements, having 
multiseriate pits on their radial walls, and separated by broad medullary 
rays. The phloem, composed of large- and small-celled elements arranged 
in radial rows, is lignified in older parts of the stem. 
(4) Cor'tex. Below the level at which this ring is established there 
may be distinguished in the internal region of the cortex — hitherto homo- 
geneous and packed with starch — patches of tissue which are differentiated 
from the rest of the cortex by the complete absence of starch. These 
patches, occurring just outside the stele, correspond topographically to the 
£ cloudy ’ tissue which occurred in preparations made by Marsh 1 of the 
stems of Stangeria paradoxa , and represent, perhaps, the same elements. 
(5) Tangential extension of xylem and phloem elements . At the 
level of the establishment of this starch-depleted tissue in the inner cortex 
a change occurs in the constitution of the central vascular cylinder, to which 
the cambium has been adding radial rows of xylem and phloem elements 
in the usual way. In this region the cells abutting on the cambium are 
longitudinally extended ; this tangential stretching, which is undoubtedly 
due to the elongation in a tangential direction of the cambial cells themselves, 
becomes greater as each succeeding element of xylem and phloem is 
differentiated, until a central cylinder is established which consists, on the 
side abutting the pith, of the usual radial rows of tracheides, but of which the 
peripheral xylem runs in a tangential direction round the stem (Plate XXII, 
Fig. II). The width of these two xylem bands becomes approximately 
equal. The phloem participates equally in this peculiar method of growth, 
so that abutting on the cambium externally are tangentially running 
phloem and phloem fibres. This gradually gives place to the earlier-formed, 
normally-directed phloem, and then to the lignified fibres which form the 
1 Marsh : loc. cit. 
P p 2 
