THE SKELETON OF THE PLANT 55 
exterior and the metabolic tissue of the cortex of stems, 
thus cutting off the intercellular space system of the latter 
from access to the air, they are usually penetrated by special 
structures known as lenticels. These are made up of corky 
cells very loosely arranged, and consequently set up the 
communication needed (fig. 47). During the winter a 
layer of cork is formed below the lenticel. 
In the corky cell-wall the cutin is frequently associated 
with a certain amount of lignin. 
The thin corky walls possess almost exactly the same 
physical properties as the thickened cuticle of the epidermis, 
a fact which affords evidence that the primary function of 
both is the same. 
Si 
Wu i ; \ (per, 
Fic. 46.—OvtTER Portion or ConTEX 
or Youne Twice or Lime. Fic. 47.Srction or a LENTICEL. 
per, cork layer ; ph, meristem layer. f, lenticel; per, cork layer. 
Like the substance of the middle lamella, both lignin 
and cutin are soluble in warm nitric acid containing potassic 
chlorate. 
In some cases the cell-walls of the epidermal protoplasts 
are impregnated with various matters that do not proceed 
from their own disintegration. Among these are various 
‘ fatty bodies, while wax is sometimes very conspicuous. 
The bloom of such fruits ag the grape and the plum is 
composed of very fine waxy particles; the impregnation 
in their case having been so great that certain particles 
have passed beyond the walls and formed a layer on the 
outer surface. The leaves of the wax-palm show an even 
denser deposit. 
Mineral matters are also of frequent occurrence in the 
