1906] WEISS—BARK IN SASSAFRAS 441 
most conspicuous structures found in the inner bark, and are even 
more striking in appearance than those found in the outer cortex. 
In longitudinal section (fig. 6, st) they show the same outlines as in 
cross section (jig. 7) and are therefore isodiametric. Their strongly 
thickened walls show a very distinct 
lamination and their contracted cavi- 
ties are connected by numerous 
simple and branched pits. Prob- 
ably on account of poor material, 
these stone cells were not seen by 
MOLLER. 
The phellogen and its derivatives. 
The derivatives cf the phellogen 
are the lenticels, the cork, and the 
phelloderm. The lenticel phellogen 
is the first to make its appearance; 
the primary cork phellogen is, at 
least in part, a direct extension of Fis. 7.—Stone cells from inner bark, 
the lenticel phellogen; and the suc- ‘S S*HO™ *45° 
ceeding phellogens arise more or less independently from the deeper 
layers of the bark. The primary cork phellogen first appears on 
the south side of an erect stem and normally on the upper surface 
of a horizontal branch. From these regions it gradually extends 
laterally and usually forms a complete layer in the course of three or 
four years. The development, however, follows no definite rule. 
For example, in one eight-year old stem there was no cork on the 
north side except in the immediate vicinity of the lenticels, while in 
another stem of the same age there were five layers of cork on the 
South side and three on the north. These observations show that 
a phellogen layer may be active in one part although it has ceased 
to be functional in another. They also show that there is no definite 
relationship between the age of the stem or branch and the number 
of layers of phellogen. The early appearance of cork in the regions 
exposed to the sun is probably due to the fact that the sassafras is an 
intolerant species and that the cork protects the deeper tissues from 
Sun scalding. 
