Bowenia spectabilis , Hook. f. 479 
those of the outer cortex, and also several of the pericycle- 
cells, are filled with cluster-crystals of calcium oxalate. 
Stone-cells are rarely met with in the root. 
Increase in thickness in the root is largely due to an 
irregular division of the cells of the ground-tissue. In the 
upper part of the root this primary thickening is especially 
obvious, particularly in the pith, and takes place to such 
an extent that the vascular bundles become considerably 
displaced. 
A phellogen-layer appears in the outer cortex in the 
young root, before secondary thickening commences. This 
is quickly followed by a second layer of phellogen which 
arises in the pericycle immediately beneath the endodermis. 
All the tissue outside the inner periderm is quickly cast 
off. This corresponds with Reinke’s observation on the 
formation of two periderm-layers in the root of Cycas 
circinalis 1 . A similar condition has also been observed by 
Gregg in the root of Cycas revoluta 2 . 
Secondary thickening occurs in a normal manner. Cambium 
first appears as an arc on the inner side of each group of 
phloem (Fig. 5). The ring of cambium enclosing the xylem - 
masses is soon completed, and simultaneously with this the 
second phellogen-layer commences to be formed in the 
pericycle. 
As in other Cycads, the cambium-layer gives rise, not 
to homogeneous masses of xylem and phloem, but to radially- 
extended plates more or less widely separated from one 
another by medullary rays. 
Secondary tracheids are produced more plentifully on the 
flanks of the masses of phloem, in the immediate neighbour- 
hood of the primary xylem groups (Fig. 6, xy. 2 ). A few 
tracheids are also formed inside the cambium-ring opposite 
the plates of secondary phloem. The secondary phloem is 
composed of radial plates, about four cells wide, each of 
1 Reinke, Morphologische Abhandlungen. Leipzig, 1873, p. 19. 
2 Gregg, Anomalous Thickening in the Root of Cycas Seemanni , Ann. Bot, 
Vol. i, 1887, P* 64, footnote. 
