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BOWMAN: MECHANICAL TISSUE IN CERTAIN VINES 367 
folia (L.) Greene, Vitis vinifera L., Hedera Helix L., Akebia quinata 
L., Rosa polyantha L., Lycium halimifolium Mill., Wisteria frutes- 
cens (L.) Poir., Lonicera japonica Thunb., Tecoma radicans (L.) 
DC., Rubus occidentalis L., and Kerria japonica L. 
The Lonicera was first examined and, as de Bary (1, p. 532) 
observed, this plant has a simple arrangement of its tissues, pro- 
ducing one zone of bast fibers and one of soft bast each year. This 
inner zone is just on the inner boundary of the bast and the wood 
fibers are disseminated in the xylem in single radial rows. The 
arrangement of fibrous strands gives sufficient tensile strength but 
is not enough to permit the plant to stand upright. These bast 
strands are not close enough together to give adequate support in 
an upright position. Under the epidermis the cortical parenchyma 
is somewhat thickened but as a source of mechanical support this 
is almost negligible. The wood cambium consists of ordinary 
parenchyma. Inside the soft bast zone between it and the pith 
there is a parenchymatous tissue called by Strasburger vascular 
parenchyma. This may give some support, particularly under a 
tension. The vascular elements occupy the remaining space. In 
older stems of the Lonicera of course the secondary tissues give 
considerable stability to the stem, but the primary xylem of a 
first year stem is not nearly enough to enable the stem to main- 
tain a perpendicular position. 
The stem of the Akebia is angled and for each ridge there is a 
large vascular bundle, oval in cross section. The bundles fill most 
of the space in transverse section. The most important mechanical 
tissue is the bast, which forms a small cushion, four or five cells 
in thickness, on the outer edge of each bundle. The bast fibers 
are heavy and have very small lumina but they are deficient in 
number. The cortical parenchyma is assimilative in the Akebia 
and therefore has very thin walls. The primary xylem is not im- 
portant from a mechanical standpoint in this plant; the conduct- 
ive elements occupy 58.3 per cent, while the mechanical tissue 
occupies only 8.3 per cent of the transverse area, i. €., a ratio 
of 7 tor. The bast cells in the Akebia are thicker thaa those 
of the Lonicera but the numerical proportion is smaller. 
In Hedera Helix the most noticeable feature is the narrowness 
of the medullary rays, which are only one cell thick. The mechan- 
