wall of the original fiber-tracheid, although the delicate 
nature of the septum made inadequate the use of chemical 
tests and polarized light to determine definitely whether 
the septum is formed only of intercellular cement sub- 
stance or whether it consists of the intercellular substance 
and two adjacent primary walls. 
The septate condition of these fiber-tracheids may 
be distinguished in radial, tangential and oceasionally in 
transverse sections. As far as can be determined, the 
formation of septa is not confined to any particular region, 
but may occur in any part of the secondary wood formed 
during a single growing season. Septa and nuclei are 
apparent in most of the fiber-tracheids. However, the 
mitotic figures associated with the formation of septa are 
infrequent. 
The original fiber-tracheid has now become, by the 
formation ofa septum, aseptate fiber-tracheid containing 
two nuclei within the confines of the original cell walls. 
It has been suggested (14) that the presence of septa in 
fiber-tracheids indicates a stage ‘‘intermediate to paren- 
chyma rather than to tracheal elements,’ but according 
to Bailey (7) internal septation, while not a ‘‘character- 
istic of fibers,”* is also not evidence of transition to pa- 
renchyma. This is true because of the fundamental 
difference in the ontogeny of the cell and the constitution 
of the secondary walls. Our evidence supports this last 
assertion, because in their ontogeny and later develop- 
ment these cells are true fiber-tracheids with character- 
istic secondary walls. The internal septations are a later 
development, which in no way alters the fundamental 
nature of the original cell. It is apparent that the funda- 
mental difference between the formation of certain pa- 
renchyma and tracheal elements is one of the timing of 
division, which may or may not be characteristic of de- 
velopment and maturation of the cells within a species. 
[174 ] 
