FLAX-STEM ANATOMY IN RELATION TO RETTING. 7 
distinctly retard retting, indicating that the bacteria enter less 
readily through the epidermis than at the stem ends. ‘These con- 
clusions were drawn from the following experiment: 
DETERMINING THE MODE OF ENTRANCE OF BACTERIA INTO THE RETTING FLAX STEM. 
This experiment was made with the advice and assistance of R. A. Tweed 
and Miss Antoinette Trevithick in the department of bacteriology, Michigan 
Agricultural College, East Lansing, Mich. 
Two sets of test tubes containing both sterilized and unsterilized straw were 
set up in series of six. Both the tops and the bottoms of the straw in three of 
each set were paraflfined, while the other three were unparaffined. One set of 
six was inocculated and incubated under anaerobic conditions and the other 
under aerobic conditions for nine days at 30° C. After this period the straw 
was examined, and it was found that the fiber was weak and overretted in the 
case of the unparaffined in both aerobic and anaerobic sets. The paraffined sets 
showed the fiber to be strong and well retted under both aerobic and anaerobic 
conditions. These resultS were similar with both sterilized and unsterilized 
straw. 
This experiment was run on four different occasions, the only difference be- 
ing that unsterilized straw, as well as sterilized straw, and an aerobic culture 
were used in the first experiment while sterilized straw only and a facultative 
anaerobic culture were used in the other three experiments. 
The results just described would indicate that the paraffined ends 
obstructed the entrance of the bacteria and retarded retting. As the 
culture used in three of the experiments consisted of a facultative 
organism, the results would further indicate that the retardation in 
retting was due to obstruction of the entrance to bacteria rather than 
the obstruction of the entrance to air. Inasmuch as the unparaffined 
sets retted more-rapidly than the paraffined sets, it would indicate 
that the bacteria found more ready means of access through the ends 
of the stem than through the epidermis. 
As the flax stems are but loosely filled with pith and are nearly hol- 
low it is reasonable to assume that they contain a large quantity of 
air relative to the quantity present in the retting water in the test 
tubes. This would tend to disprove that the restriction in the air cir- 
culation was responsible for the retardation in retting. 
The bacteria enter the flax stems through the broken ends of the 
roots; the inside of the flax stem is but loosely filled with pith cells 
at the center and is nearly hollow, so that once inside the root ends, 
the retting liquid containing the bacteria can find ready access 
through the entire length of the stem. The bacteria can then pass 
out into the cambium layer along the medullary rays between the 
sectors of wood or xylem. The cambium layer is thus most accessible 
to the attack of the bacteria, because it lies nearest the pith of the 
stem where bacteria find their way unobstructed and the almost com- 
plete waterproof covering on the outside of the stem forces the bac- 
teria to first attack the ‘stem from the inside and adjacent to the 
ecambium layer. The cambium layer forms an unbroken cone running 
the full length of the stem excepting at the nodes, where the leaf 
scars interrupt its continuity. 
The area that is next disintegrated by the bacteria is that occu- 
pied by the phloem parenchyma, - which lies between the fiber bundles 
and cambium layer (tissue 2, in fig. 2). The inside surfaces 
of fiber bundles, when well retted, are “nearly always more lustrous 
than the outside surfaces, indicating that the inside surfaces, lying 
