486 Pearson. — Anatomy of the Seedling of 
abundant higher up the petiole (cf. Fig. 18), have appeared. 
The general ground-tissue consists of parenchymatous starch- 
containing cells, among which are scattered numerous muci- 
lage-canals, particularly in the neighbourhood of the bundles 
(Fig. 1 6,#/. c.); these are continuous with the canals of the 
stem, and higher up unite to form the single central canal of 
the petiole (Fig. 17, m. c.). Numerous cells containing cluster- 
crystals of calcium oxalate are present, especially in the 
phelloderm. In the upper part of the leaf-base an irregularly- 
arranged band of stereome appears in the peripheral cortical 
tissue, and afterwards attains a greater development in the 
petiole. 
No periderm is formed in the petiole. The epidermis and 
two layers of cells immediately beneath it are composed of 
very thick-walled cuticularized cells, forming a peripheral 
band of stereome which is interrupted by stomata (Fig. 17). 
Beneath it is an irregularly-arranged band of stereome, con- 
tinuous with the similar band in the leaf-base. The vascular 
bundles of the leaf-base have undergone some fusion, and the 
petiole contains, usually, four resulting bundles which are 
orientated towards the centre, around the single central 
mucilage-canal (Fig. 17). The vascular bundle contains some 
centripetal wood (Fig. 18, cp. xy.\ which increases in quantity 
towards the upper end of the petiole (Fig. 19, cp. xyi). The 
protophloem is represented by a wide band of collapsed tissue 
(p. phi). In the secondary petiole the bundle shows a still 
further increase of centripetal wood, and decrease in number 
of centrifugal elements. This preponderance of centripetal 
over centrifugal elements increases in the higher parts of the 
bundle until, in the lamina itself, the xylem is almost entirely 
centripetal, centrifugal elements being absent or one or two 
only (Fig. 20). Transfusion-tissue is possibly represented by 
one or two more or less transversely-elongated elements on 
the flanks of the centripetal xylem, which however do not 
show the markings characteristic of that tissue (Fig. 20, tfi). 
The inconspicuous character of these elements may of course 
be attributed to the age of the leaf : no old leaves were 
