403 
Scott. — On Peduncle of Cycadctceae. 
diameter (see Figs. 3, 4, 5, and 7). The compound sieve- 
plates, chiefly on their radial walls, come out very clearly 
under appropriate treatment. 
The small albuminous cells, which in Gymnosperms repre- 
sent functionally the companion-cells of the higher plants 1 , 
are very conspicuous, often forming regular tangential bands. 
On the outer side of the bundle is a band of crushed tissue, 
consisting of the obliterated elements of the first formed bast, 
or protophloem. Beyond this there is a small-celled paren- 
chymatous tissue, which is no doubt to be regarded as 
pericycle. This tissue retains the power of cell-division for 
a long time, and occasionally gives rise to anomalous forma- 
tions in connexion with the older bundles. 
On the inner side of each bundle is a considerable mass of 
small, rather thin-walled cells, with conspicuous nuclei, forming 
a group easily distinguishable from the large-celled tissue 
of the pith (Figs. 4 and 5,^). This group is similar in structure 
to the pericycle, with which it is in fact connected, round the 
sides of the bundle. It no doubt comes under the category 
of M. Flot’s internal pericycle, or ‘zone perimedullaire,’ the 
present case being one of those in which this zone is only 
differentiated in connexion with each separate bundle 2 . It 
is in this tissue that the centripetal xylem is developed. 
Centripetal wood. The longitudinal distribution of the 
centripetal xylem is as follows : it is absent from the actual 
base of the peduncle, but begins to appear a little higher up, 
in the region where the irregularity of the vascular ring is 
most marked (see Fig. 2 x 1 ). Above this point it rapidly 
increases in amount, and then maintains about the same 
degree of development throughout the greater part of the 
peduncle, in the region where the arrangement and orientation 
of the bundles is normal ; in the axis of the cone itself the 
centripetal xylem again diminishes in amount, disappearing 
1 Strasburger, Histologische Beitrage, III, pp. 154, 157. 
2 See Flot, Recherches sur la zone perimedullaire : Ann. des Sci. Nat. (Bot.), 
Ser. 7, T. 18, p. 107, 1893. For linguistic reasons it seems desirable to substitute 
circummedullary for perimedullary . 
