1888. | BOTANICAL GAZETTE, 253 
or the phloem produced by the cambium ring after it is com- 
pleted around the stem. 
Difficult as it is to harmonize the different ways of de- 
scribing the processes of periderm formation, as given by 
various writers, nearly all agree in the main features of that 
by which bark is produced, viz: bark is the product of the 
internal or deep-seated periderm, and it consists of all that 
portion of rind-tissue outside of this periderm, which tissue, 
cut off from nourishment by the corky layers of periderm, 
dies and is eventually thrown off. This is the Borke of the 
Germans and the ecorce crevassée of the French.1! One 
form of internal periderm originates from phellogen cells 
extending in a nearly continuous layer around the stem; this 
Sives rise to the so-called ring-bark, examples of which are 
Vitis and Clematis. Another form,of internal periderm 
arises deeper in the rind of certain stems on which there 1s 
already a superficial periderm. Th 
circumference, arise in such a manner that, as De Bar ex- 
of periderm for 
ed formation of 
ence the two kinds, ring- 
the definition of bark given by De Bary?’, 
all those trees from the list of bake 
not have, at some period, one of the two 
Periderm. He quotes this de 
or two previous he gives 
ng trees among 
d he expressly 
the soar : ned, an 
ecimens which he examinee, ‘ 
States that these 83 kinds possessed internal or secondary 
Periderms, : 
: of superficial 
pected sy Yack of 
ow, according to De Bary’s expla 
te 
rla 3d edition et anno 
par praite de Botanique par J. Sachs. Traduit de Vallemand su 
Fh. von Tieghem. 1874. 
*Comp. Anat. p, 551 
