26 BULLETIN 1185, U. S. DEPARTMENT OF AGRICULTURE. 
heved desirable to supplement the leaf-scar test with the epidermis 
test, so that when a positive leaf-scar test is secured the epidermis 
test also may be used to determine whether retting has proceeded 
far enough to thoroughly loosen the epidermis. In case the epider- 
mis test does not confirm the positive leaf-scar test the retting may 
be allowed to proceed still farther until a positive epidermis test 
is secured. It is thought that the leaf-scar and epidermis tests are 
distinctly more reliable than the loose-core test and that even where 
the dry-straw test is used they may be of some value as indicating 
when to begin the dry-straw tests. 
SUMMARY. 
The present method for testing wet flax stems for completion of 
retting is not dependable. 
Variations in straw quality may interfere with securing a good ret, 
and therefore stems of uniform diameter and fiber quality are de- 
sired. 
Retting proceeds from the cambium layer toward the outside of the 
stem. The cuticle and the leaf scars form a waterproof covering for 
the entire outside of the stem except the stomata. The order in which 
the cortical tissues are retted depends upon their proximity to the 
cambium layer as well as on the solubility and thickness of the pectin 
layers in the different tissues. 
The changes in the flax stem visible to the naked eye and most 
closely associated with the completion of retting are disintegration 
of the leaf scars, the mechanical separation of the cuticle,and the 
separation of the fiber bundles from the rest of the cortex. 
The mechanical test made on wet flax stems by pulling the girth 
of cortex away from the wooden core at right angles to the stem and 
starting near the root end is easily made by inexperienced workers, 
because the resistance to separation at the nodes is marked. This 
type of leaf-scar test is more dependable than the loose-core test now 
in common use for deciding when retting is completed. 
The dependability of the leaf-scar test may be increased by sup- 
plementing it with the epidermis test, in which the loosened cortex is 
moved to and fro in clear water in order to observe whether the 
cuticle is thoroughly loosened and the fibers sufficiently divided. 
5 ler ahaa tho Binh pails sian Pee «Sop ge. 
