FLAX-STEM ANATOMY IN RELATION TO RETTING. 9 
tions with the microscope of cross sections made at the end of this 
stage in retting show that the fiber bundles, outer parenchyma, and 
epidermis are intact and that the parenchyma between the fiber bun- 
dles has been destroyed. 
The relation of the thickness of the pectin layer to the retting pe- 
riod is indicated by the shorter retting period of small stems. Stems 
1.5 to 2 millimeters in diameter take 12 to 36 hours longer to ret than 
stems varying from 1 to 1.5 millimeters in diameter. The larger 
stems have thicker layers of pectin. The panicle end, which is the 
small end of the stem, rets before the root end of the stem, where the 
pectin layer is relatively thick. 
As soon as the parenchyma between the fiber bundles is destroved 
the retting liquid and bacteria surround the bundles on all sides 
excepting the outer sur- 
faces that le next to 
the outer parenchyma. 
According to Tadokoro 
the cell walls of the 
epidermis, excepting 
the cuticle, and the cell 
walls of the paren- 
chyma and the middle 
lamelle of the fiber 
cells are composed al- 
most entirely of pectin 
compounds. Hence the 
relative thickness*® of 
the walls of these tis- 
sues as compared with 
each other and with the 
middle lamelle of the 
fiber cells give some 
idea as to the time it 
should take to break 
down these tissues in 
Fic. 4.—Changes in the appearance of the cortex of 
the retting process. A va opens the last BIE of eee. The cortex 
: 3 : ‘ is here shown separate rom the wooden core, but 
study of Figure 2 still almost intact. 10. 
shows: that the pectin 
layer is thickest in the fiber bundles, followed in order by the epider- 
mis and outer parenchyma. The phloem parenchyma and that lying 
between the fiber bundles have pectin layers of about equal thickness 
but somewhat thinner than that of the outer parenchyma. Of all the 
tissues the cambium has the thinnest layer of pectin. 
Since the layer of pectin in the cell walls of the epidermis is thicker 
than that in the outer parenchyma it would naturally be expected 
that the epidermis would not be destroyed until after the outer 
parenchyma. ‘The path of bacterial activity is directed against the 
outer parenchyma, and microscopic examination shows that those 
portions of the outer parenchyma lying next to the spaces between 
the bundles are destroyed next (tissue 4, in fig. 2), leaving only the 
strips of outer parenchyma that are found in the middle of the outer 
surfaces of the bundles intact. The reason for this is that the bac- 
® Tadokoro, T. Op. cit., p. 37. 
55D159—23 2 
