PERIDERM. 187 
Finally, the so-called inner hairs may also be mentioned, 
which occasionally penetrate into the air-cavities (star-shaped 
hairs of the Nymphe, glandular hairs of Aspidium Filix mas, 
Fig. 162). 
The epidermis no longer suffices for older plant organs of 
several years’ growth, since it is a much too delicate tissue (for 
instance, for the stems and branches), and, as permanent tissue, 
is not capable of keeping pace with the growth in thickness, 
In these organs, therefore, there is formed beneath the epi- 
dermis, and mostly independent thereof, another tissue, the 
periderm.' The latter consists of a permanent tissue, the 
cork, and a formative tissue, the phellogen,’ or cork-cam- 
bium. 
The phellogen, by a tangential division of its cells, forms the 
Fic. 97.—Cells from the phelloderm of the bark of Canella alba (J. Moeller). 
cork-cells; but it is also capable of contributing to the increase 
of the bark parenchyma by the formation of parenchymatous 
elements. Sanio* terms the aggregate of cells which are thus 
produced, and occasionally thickened on one side (Figs. 97, 149) 
phelloderm * or cork layer of the bark. 
1 epi around, and dépuc skin. 
? PedAos cork, and yevvaw I produce. 
3«*Bau und Entwickelung des Korkes,” Pringsheim’s Jahrb., ii., 
(1860), 47. H. v. Mohl, ‘‘ Entwickelung des Korkes und der Borke der 
baumartigen Dicotylen” (1836). ‘‘ Verm. Schrift.,” Tibingen, 1845, 
225. F. von Hohnel, ‘‘ Ueber Kork und verkorkte Gewebe tiberhaupt.” 
Sitzungsberichte der Wiener Akademie, 76 (1877). Hanstein, “ Bau und — 
Entwickelung der Baumrinde.” Berlin, 1853. Hofmeister, ‘ Handbuch 
der phys. Botanik,” i., 252. De Bary, ‘‘ Anatomie.” 
* PedAos cork, and dépua skin. 
