1906] WEISS—BARK IN SASSAFRAS 443 
from the subepidermal parenchyma. In the majority of cases it 
arises from the layer of cells just inside the epidermis. Sometimes, 
however, it is derived from the second, third, or fourth layer, and this 
is always the case when stone cells are present next the epidermis. 
It thus frequently happens that the different parts of the phellogen 
do not all arise from the same layer of cells. The secondary layers 
of phellogen are largely derived from the parenchyma cells in the 
secondary phloem. When stone cells are present in the parenchyma 
the phellogen often bounds them on the inside. The phellogen forms 
concentric layers in the stem, but these layers are not altogether 
independent. In certain regions two layers will coalesce, in other 
regions they will be separated from each other by several layers of 
cells. Even the outermost of the secondary phellogens is more or 
less united with the primary phellogen. 
The cork, as already noted by MOLLER, is of the ordinary type. 
It consists of empty cells arranged in radial rows, and the walls are 
thin and suberised ( jigs. 5, 6, 9, c). In most cases from ten to twelve 
layers are formed by each phellogen. The structure of the cork is not 
uniform throughout the Lauraceae; in certain genera it consists of 
two kinds of cells arranged in more or less definite layers; namely, 
thin-walled cells and cells in which the inner tangential walls are 
thickened.5 
- The phelloderm in the sassafras forms a most characteristic feat- 
ure of the bark. When derived from secondary phellogens it con- 
sists almost entirely of strongly flattened cells with thick lignified 
walls, provided with simple and branched pits. The flattening is in 
a radial direction, and the cells show the same rectangular outlines 
in both radial and transverse sections (figs. 5, 6, phel). The phel- 
loderm is arranged in layers from one to three cells thick. The layer 
derived from the primary phellogen differs from the others in being 
composed of both thin-walled and thick-walled cells. In the case of 
lenticels the thick-walled phelloderm cells are few and scattered and 
are sometimes absent altogether. Lignified phelloderm does not 
seem to be of very frequent occurrence. According to J. E. Wetss® 
it is to be found in species of Cytisus and Philadelphus; KUHLA’ 
5 See MOLLER, Anat. der Baumrinden 103 
. 1882. 
© Beitrage zur Kenntniss der Korkbildung. Seiten. K®6nigl. Bayer. Bot.Gesells. 
6:61. 1890. 
7 Bot. Centralbl. '71:196. 1897. 
