Vegetative Anatomy — Carlquist 
205 
stage in specialization may be represented 
by D. watalealae. 
5. D. watalealae (Fig. 22, right). Pith entirely 
thin walled, with large intercellular spaces; 
no secretory canals present; carbonized 
resin deposits in intercellular spaces. 
The pith of Arg^roxiphium Caliginii (Fig. 
19) is highly lacunose, and carbonized resin 
deposits are present. The inner margins of 
vascular bundles are clothed with a con- 
spicuous zone of very thick- walled fibers. The 
remainder of the pith, however, remains thin 
walled and unlignified. An identical condition 
occurs in A. Grayanum. Wilkesia differs only 
in lacking carbonized resin deposits. 
The pith of Arg^roxiphtum sandwkhense 
(Fig. 20), however, shows a remarkable anom- 
alous feature. Basically, pith in this species is 
identical with that of A. Caliginii in that it is 
lacunose and has fibrous caps on inner faces 
of the bundles. Into the large intercellular 
spaces of the cells of mature pith, however, 
new cells are proliferated by pre-existing pith 
cells. These new cells subdivide in various 
planes, often forming packets oriented in a 
particular direction. Most of these packets 
mature into sclerified cells (Fig. 20, right) al- 
though some of them (Fig. 20, left) appar- 
ently remain thin walled. Some of these scle- 
rified cells, although somewhat elongate and 
fiberlike, have simple pits and should prob- 
ably be termed sclereids. Others, as the inset 
in Figure 20 shows, have bordered pits and 
must therefore be termed tracheids. However, 
because Compositae do not have tracheids in 
the proper sense in their xylem, these trache- 
ids are perhaps more nearly comparable to 
the "vascular tracheids" (i.e., degenerate ves- 
sels which lack perforation plates) which do 
occur in the secondary xylem of A. sand- 
wichense (Carlquist, 1958). For the phenom- 
enon described above, the term "pith tra- 
cheid" might be invented to accomodate 
their distinctive origin and mode of occur- 
rence. The formation of these pith tracheids 
might be likened to the formation of tra- 
cheids in callus, such as those which occurred 
in the experiments of Wetmore and Sorokin 
(1955). The formation of nests of sclereids 
and pith tracheids in A, sandwkhense pith, 
however, is apparently not related to pre- 
existing vascular tissue, with which the pith 
tracheids are not in continuity. The formation 
of these nests is centripetal: the central por- 
tion of the pith was observed to contain only 
thin- walled cells, whereas such packets have 
matured into sclereids and tracheids near the 
periphery of the pith. A given nest may con- 
tain tracheids only, sclereids only, or a mix- 
ture of the two cell types. As in the experi- 
ments of Wetmore and Sorokin, no phloem 
could be detected in association with the 
pith tracheids. 
Although the diversity of pith types in 
Dubautia is considerable, the pith of Arg^ro- 
xiphium and Wilkesia does not match that of 
any given species of Dubautia. The presence 
of certain features, such as carbonized resins, 
is very similar, and pith of Argyroxiphium and 
Wilkesia can be considered to be within the 
range of the variation pattern of Dubautia pith. 
Stem 
The structure of the stem in respects other 
than nodal anatomy and pith anatomy is 
relatively uniform within Dubautia, Argyro- 
xiphium, and Wilkesia, so that a small num- 
ber of examples may be used, and variations 
may be described where they occur. In Du- 
bautia Menziesii (Fig. 21), the vascular bun- 
dles develop prominent bundle caps of proto- 
phloem fibers. The layer of cells immediately 
exterior to the fibers is a well-marked endo- 
dermis (Fig. 21, inset) in which a Casparian 
strip may easily be demonstrated. The endo- 
dermis accompanies the bundle cap of a leaf 
trace in its departure from the vascular cylin- 
der, although no endodermis occurs in leaf 
base or leaf. Although stem endodermis is 
uncommon in dicotyledons at large, it is 
frequent in Compositae, as the data of Met- 
calfe and Chalk (1950: 788) and Carlquist 
( 19570 ' 47) show. Numerous secretory canals 
are arranged adjacent to the vascular bundles. 
