Vegetative Anatomy — Carlquist 
207 
Although the secretory canals appear at first 
glance to be arranged at random, examination 
of serial sections shows that they occur in 
pairs beside larger bundles which, farther up 
the stem, depart from the vascular cylinder as 
leaf traces. Cortical secretory canals, then, are 
initiated continuously with growth in length 
of the stem, because departure of secretory 
canals in association with leaf traces would 
result in their total absence in upper portions 
of a stem if new ones were not initiated. In 
D. Menziesii, cortical secretory canals con- 
tinue into the leaf base for a short distance, 
although distal portions of the leaf lack them. 
In species which characteristically have such 
canals in the lamina, such as D. Knudsenii 
(Fig. 1), these canals continue from the stem 
into the leaf and either ramify or (particularly 
in the case of canals adaxial to veins) originate 
de novo. As the portion of a cleared leaf of D. 
lonchophylla in Figure 6 shows, these canals 
mainly parallel the larger longitudinally ori- 
ented veins. The cortex of D. Menziesit ex- 
terior to the secretory canals is highly lacu- 
nate. In the stem shown in Figure 21, cork 
formation is beginning. Periclinal divisions 
may be seen both in the epidermis and in the 
layer immediately beneath the epidermis. Cork 
formation, then is not restricted to a single 
layer of the stem. At extreme left in Figure 21, 
two degenerating biseriate glandular hairs 
may be seen. 
The stem of D. waialealae (Fig. 22) illus- 
trates several points of contrast. Only small 
lacunae are present in the cortex (gaps in that 
region in Fig. 22 probably resulted from the 
fact that a dried specimen was used for this 
preparation). Secretory canals are infrequent, 
although a small canal may be seen below the 
large bundle cap, lower right. Cork formation 
is not initiated in the epidermis, which is al- 
most entirely involved in the formation of 
trichomes, but may be seen in the two or three 
cell layers below the epidermis. As in D. 
Menziesit, therefore, cork formation is not 
limited to a single layer. The hairs which 
thickly clothe the stem of D. waialealae are 
nonglandular and uniseriate in their upper 
portions. The multicellular nature of the 
trichome base results from elongation of epi- 
dermal cells subtending the hair. The tri- 
chome proper, therefore, may be termed 
uniseriate. 
The differences between D. Menziesii and 
D. waialealae mentioned above are not great, 
and represent the extremes of variation ob- 
served in the genus. The majority of the spe- 
cies have moderately lacunate cortex, inter- 
mediate between these two types. Although 
secretory canals were found to be scarce or 
lacking in the stems of D. waialealae and D. 
platyphylla examined, they are present to some 
extent in the remaining species. 
In the aspects of stem structure mentioned 
above, Argyroxiphium and Wilkesia are refera- 
ble to exactly the same pattern. In Argyro- 
xiphium, carbonized resin deposits, like those 
of the pith, occur in intercellular spaces in the 
cortex, as well as between fibers in bundle 
caps. Argyroxiphium Caliginii is the only spe- 
cies of its genus in which secretory canals are 
present in the leaves (Carlquist, 1957V): secre- 
tory canals accompanying leaf traces continue 
into the leaves. In other species, they termi- 
nate below the level at which leaf traces enter 
leaf bases. In Wilkesia, which also lacks foliar 
secretory canals, many of the leaf traces are 
not accompanied by secretory canals, al- 
though canals are abundant around the vas- 
cular cylinder proper. Secretory canals in 
Wilkesia, for the most part, terminate below 
separation of leaf traces from the cylinder. 
Abundant cork formation from subepider- 
mal layers is characteristic of Argyroxiphium 
Caliginii and A. Grayanum, whereas little 
cork occurs in the rosette species A. sand- 
Figs. 21-23. Transections of stems of Duhautia. (21) D. Menziesit; epidermis at left; X 98; inset shows endo- 
dermis with Casparian strip (line running through cells above fibers), X 350. (22) D. waialealae, X 115. (23) 
D. platyphylla; stem showing secondary growth; cork above, secondary phloem below; X 107; inset shows an 
area of lacunate cortex, enlarged, in which pectic warts are present on cell walls, X 218. 
