Genus Statice as represented at Blakeney Point . /. 259 
very large thin-walled cells (/), and the radial and outer walls of the 
piliferous layer (p.l) are thickened and suberized. The structure of a 
typical seedling root is shown in Text-fig. 9. 
At a very early age, while the seedling is still in the cotyledon 
stage, secondary growth begins, and secondary xylem, consisting of pitted 
vessels in which, in longitudinal section, the cross-walls are often persis- 
tent, and lignified fibres are produced, resulting in the production of a 
strongly lignified core. No parenchyma elements are present in the wood 
of a typical binervosa root, and some idea of the nature of the xylem 
may be obtained from Text-fig. 10. Medullary rays are absent except 
Text-fig. 9. Transverse section of a root of S. binervosa. 
pxy. = protoxylem ; ph . = phloem ; per. = pericycle ; end. — 
endodermis ; l. = large cells of the cortex ; p.l. = suberized 
piliferous layer, x 300. 
Text-fig. 10. Transverse section 
of part of the xylem of the root of S. 
binervosa. Main bank plant, x 236. 
v. = vessels ; f. = fibres. 
in the region of the exit of a root-trace, where a multiseriate ray is 
developed. 
Annual rings are usually well marked (cf. Text-fig. n). The secon- 
dary phloem is small in amount, and shows no features of special interest. 
Simultaneously with the beginning of secondary growth, the pericyclic 
cells become meristematic, and the cambium thus produced gives rise 
to a periderm on its outer margin, thus cutting off the endodermis and 
cortex. 
This periderm is composed of three to four layers ; of thickish walled 
cells with dense homogeneous contents. The contents are of the nature 
of tannin, and may possibly be a Phlobaphene — a decomposition product of 
plumbagin — the substance stated to occur in the roots of the Plumbagi- 
naceae. Practically no information could be obtained as to the nature 
of plumbagin, which is described by Tunmann 1 as ‘ ein wenig erforschtey 
1 Tunmann, O. : Pflanzenmikrochemie, Berlin, 1913. 
