136 Curtis. — The Anatomy of the Six Epiphytic 
in the ring of sclerenchyma are smaller than those lying in the conjunctive 
tissue. The phloem of all the strands is protected by fibres whose walls 
bear several striations. Fibrous elements may be absent from the periphery 
of the xylem. If present, they usually have larger lumina and contain 
starch. Small and large spiral vessels are to be seen in the xylem, and 
tracheides, especially those with equidistant pits, are of frequent occurrence. 
The branch is of one order only, and bears about six leaves at an inch 
or an inch and a half apart. The leaf is continued below in an unbroken 
sheath to its node where the next lower blade bends out from its sheath. 
The sheaths are dull in colour, with regular lines or irregular groups 
of darker brown, due to the complete or partial discoloration of the many 
sclerenchymatous strands running parallel to the surface (PL VIII, Fig. 18). 
Only the largest of these strands contain vascular bundles, and many of the 
fibres are devoid of contents. The cells of the general tissue of the sheath 
are strewn with so many large pits of irregular shape that a reticulate 
appearance is lent to the walls. This is most noticeable in the spindle-like 
cells which adjoin or cross the large canals lying between the strands of 
sclerenchyma. Each of these cells contains a spherical crystal aggregate. 
Only two or three elements are present in the phloem and xylem of the 
vascular bundles. 
The branch is oval in transverse section. Its cortex is narrow, but 
within it is a wide band of sclerenchyma in which are embedded most 
of the vascular bundles. Only a few strands occur in the ground tissue. 
A heavy cuticle covers the free surface of the small epidermal cells. The 
outer cells of the cortex are cutinized, but the inner are of cellulose. All 
are pitted and elongated in longitudinal section and most contain starch. 
The vascular bundles in the sclerenchymatous ring are seldom large. 
Usually about six elements are present in xylem and phloem. Those 
of the central portion of the branch are well developed and may have com- 
plete sheaths of sclerenchyma. More often this is absent on the side of the 
xylem, but two or three cells deep on that of the phloem. The cells of the 
ground tissue, which are oval in transverse and elongated in longitudinal 
section, are filled with dense masses of starch. 
The leaf is strengthened by the presence of much sclerenchyma 
(PL VIII, Fig. 24). All the bundles are surrounded by large fibrous sheaths ; 
numerous sclerenchymatous strands run immediately within the two 
epidermes, especially the upper ; and a broad strand is present at the edge 
of the leaf. The isolated strands near the epidermes consist of. from one to 
six fibres. Their contents disappear early, and few pits or striations occur 
in their walls. There are usually nineteen vascular bundles in the leaf. 
The elements of their sheaths vary in size ; near the xylem they are large 
and often without striations ; near the phloem they are smaller, striated, 
and pitted, and retain their protoplasmic contents. Most of the smaller 
