RETICULATED—SCALARIFORM—AND SIEVE VESSELS. 55. 
d. Reticulated Vessels—In these vessels the convolutions 
are more or less irregular, and connected in various ways by 
cross or oblique fibres, so as to produce a branched or netted 
appearance (fig. 112). Thes@ vessels are generally larger than 
the annular, and of much more frequent occurrence. They are 
found in similar situations. 
e. Scalariform Vessels—The peculiar appearance of these 
vessels is owing to their walls being marked by elongated trans- 
verse pits or lines, arranged over one another like the steps of a 
ladder, whence their name (jigs. 113 and 114). They are some- 
times cylindrical tubes like the other vessels, as in the Vine 
(fig. 114), and in many other Dicotyle- 
dons, in which condition they are ap- 
parently but slight modifications of re- 
ticulated vessels ; but in their more perfect 
state, scalariform vessels assume a pris- 
matic form, as in Ferns (jig. 113), of which 
they are then very characteristic, though 
sometimes they may be found elsewhere. 
The anwilar, reticulated, and scalari- 
form vessels constitute the spwrious trachee 
of some authors. These vessels have 
commonly tapering points like the true 
spiral vessels ; and thus overlap at their 
extremities when they come in contact 
(fig. 113). But in other instances they 
terminate more or less obliquely, or by 
flattened ends, like most pitted vessels. 
We frequently find in the same vessel 
one or more of the above forms combined 
with the spiral (figs. 111 and 115), and 
thus forming intermediate states of each 
other. 
f. Sieve-tubes or Sieve-vessels.—These 
are vessels in which thickening of the 
Fig. 116. 
Fig. 116. Young sieve- 
tubes or. sieve-vessels 
cell-walls of their component cells does 
not take place uniformly over their whole 
surface, but only at the ends of the cells, 
that is, where they are in contact with 
others of a similar nature. At these ends 
it forms a kind of network, sculptured in 
relief as it were on the wall (fig. 116, q); 
and when in such cases, the unthickened 
part of the walls of contiguous cells 
becomes absorbed so that their cavities 
are continuous, we have formed what 
are commonly known as sieve-tubes or sieve-vessels. 
from the longitudinal 
section of the stem of 
Cucurbita Pepo. q. 
Transverse view of 
the sieve-like partition 
walls. si. Sieve-plate on 
the side-wall. x, Thin- 
ner parts of the side- 
wall. ps. Contracted 
protoplasmic contents, 
lifted off the transverse 
septum at sp, After 
Sachs. 
Some have 
also sieve-like openings through their side walls (fig. 116, si). 
These vessels are very constantly present in the inner bark or 
