8 BULLETIN 1185, U. S. DEPARTMENT OF AGRICULTURE. 
next to the phloem parenchyma, have been subjected to the action 
of the bacteria for a longer time and that the traces of the phloem 
parenchyma have been more completely destroyed than those of the 
outer parenchyma that lies next to the outside of the fiber bundles. 
The phloem parenchyma is more accessible than the outer paren- 
chyma, since the former lies next to the cambium layer and the 
bacteria soon assimilate the small quantity of food material in the 
cambium layer. It does not take so long to destroy the phloem 
parenchyma as the outer parenchyma, because of the thinner layers 
of pectin present in the phloem parenchyma. 7 
x 
27 ue 
Fic. 3.—Fiber bundles of flax taken from the same stem, showing variations in the size, 
the shape, and the number of cells. The figures show the number of cells counted 
in each bundle. The outside edges of the bundles are uppermost. The crosses at the 
points of grooves indicate where separations would occur during retting. (Outline 
camera-lucida drawing, enlarged 140 times.) 
After the phloem parenchyma is disintegrated the bacteria and 
the enzym pectase which they secrete are found next to the inside 
surfaces of the fiber bundles and the parenchyma that hes between 
them. The fiber bundles and the strips of parenchyma between them 
may be likened to a picket fence in which the .“ pickets” or fiber 
bundles are about five times as wide as the spaces. The comparison 
holds good from the standpoint of bacterial activity; the fiber 
bundles form obstructions to the progress of the bacteria both be- 
cause the quantity of pectin present in the fiber bundles is many 
times as great as that in the areas between them and because the 
cementing substances between the fiber cells are partly woody and 
more or less impervious to the attacks of bacteria.’ HExamina- 
7 Tadokoro, T. Studies on flax retting. Jn Jour. Col. Agr. Tohoku Imp. Univy., v. 5, 
p. 84. 1913. 
