10 BULLETIN 1185, U. S. DEPARTMENT OF AGRICULTURE. 
teria have to work four or five times as far to meet at the middle of 
the outer surface of a bundle as to reach the epidermis. 
The retting fluid now incloses almost nine-tenths of the circum- 
ferences of the fiber bundles, and the fiber bundles are held together 
only by the epidermis and the small strips of outer parenchyma 
lying at the middle of the outer surfaces of the bundles and bridg- 
ing the space between the fiber bundles and epidermis. The retting 
of these two nonfibrous elements of the cortex that remain appears 
to occur almost at the same time as the separation of the fiber bundles 
into several smaller units that are known as commercial fibers, and 
when this last step 1s accomplished retting is completed. It is well 
known by flax retters that the disintegration of the epidermis occurs 
as about the last change 
in the retting process, 
and Tadokoro states 
that the cuticle is 
detached mechanically 
during the last stage 
of retting.? Whether 
these changes occur si- 
multaneously depends 
somewhat upon the 
stem diameter; in very 
coarse stems the fiber 
bundles are not sepa- 
rated into smaller units 
until some time after 
the loss of the epider- 
mis, owing probably to 
the extreme thickness 
of the pectin layers in 
the bundles. 
The fiber bundles are 
Fic. 5.—Changes in the EDD eget OF ee ee Rs composed of several 
flax during the last stages of retting. The cortex ; 
is here shown separated into a number of smaller thousand  fibe1 cells, 
girine,  Natuly aver, mera oh mereuervan. ae © gind acres ecctionam 
| one bundle will aver- 
age about 25 cells in number. The fiber bundles vary in size and shape 
and in the number of cells. Figure 3 shows camera-lucida drawings of 
the outlines of fiber bundles taken from the cross section made at the 
center of a single flax stem. Some of the bundles are three or four 
times as large as others. Some have 60 cells, some have only 25, and 
some in extreme cases only 8 or 10 cells. Flax fiber bundles are not, as 
is commonly supposed, cylindrical or elliptical in cross section. On — 
the contrary, they are irregular, being two or three to eight times as- 
broad, measured parallel to tangents drawn on the circumference of 
the stem, as the thickness of the bundles measured radially. They 
are somewhat rounding to slightly zigzag in outline on the outer 
»' Tadokoro, I. Op: cit.; p. 37. 
