If the divisions which form septa occur before the sec- 
ondary wall is laid down, a strand tracheid or a wood 
parenchyma strand would result. If the divisions occur 
after the formation of the secondary wall, aseptate fiber- 
tracheid would be the result. 
In the formation of septate fiber-tracheids there is 
also an element of timing of the division which may be 
significant. It would be interesting to know how longa 
cell may remain a nucleated fiber-tracheid before becom- 
ing a septate fiber-tracheid, and whether each nucleated 
fiber-tracheid is a potential septate fiber-tracheid. ‘This 
is significant in view of the fact that these elements have 
been used as diagnostic criteria in classification. However, 
one must emphasize the fact that it has not been deter- 
mined whether in a definite section of wood all the cells 
have reached their end point of development or have been 
stopped in some intermediate stage. Observations on 
these points by numerous workers will aid in giving a 
true significance to the use of these variable elements in 
classification. 
The occurrence of cytokinesis in the formation of 
septate fiber-tracheids distinguishes these elements from 
the truly multinucleate fibers which occur, at times, in 
the phloem. The formation of the cells under discussion 
also differs from the formation of cells by the cambial 
initials of the higher plants (1), (2), (3), (4), (5) in that, 
while the protoplasts involved are capable of divisions 
within the original cell, the resultant cells or compart- 
ments do not undergo the normal maturation pattern of 
cells derived from the cambium. 
It is held by some (9, p. 158) that the protoplast dis- 
appears during the development of the lignified secondary 
wall of tracheary elements. Fuchs (11), in discussing the 
origin of lignin, suggests that the formation of lignin 
occurs only in those cells in which the protoplasm is 
[175 ] 
