. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. 334 PRIMARy ARRANGEMENT OF TISSUES. Fig. 156. Cross-section through the vascular bundle In the midrib of the leaf of Olea Europaea (375). s-s the phloem, consisting of wide (parenchymatous ?) cells, and scattered groups of very narrow elements (sieve-tubes ?); comp. p. 3 2 5. f-f sclerenchymatous fibres, forming a girdle round the outer edge of the phloem, and occurring scattered on the inside of the xylem. The very dense xylem borders on the phloem internally; the primitive elements at its inne
. Comparative anatomy of the vegetative organs of the phanerogams and ferns;. Plant anatomy; Ferns. 334 PRIMARy ARRANGEMENT OF TISSUES. Fig. 156. Cross-section through the vascular bundle In the midrib of the leaf of Olea Europaea (375). s-s the phloem, consisting of wide (parenchymatous ?) cells, and scattered groups of very narrow elements (sieve-tubes ?); comp. p. 3 2 5. f-f sclerenchymatous fibres, forming a girdle round the outer edge of the phloem, and occurring scattered on the inside of the xylem. The very dense xylem borders on the phloem internally; the primitive elements at its inner edge do not appear clearly; its. larger external portion consists of radial rows of thick-walled pitted tracheae, which alternate with bands of parenchyma. The latter are indicated by the granular dotting of the lumen, p paren- Fig. 157, Cross-section through a vascular bundle in the leaf of Welwitschia mirabilis (145). An uninterrupted zone of very thick-walled and elongated sclerenchymatous fibres surrounds at / the outer edge of the phloem, and at /' the inner edge of the xylem. Inside the zone/follows the phloem,which is crescent-shaped in cross-section, consisting of narrow, radially arranged, elongated elements; their structure could not be detected with certainty, nor are they drawn quite accurately in the figure, because the great swelling of the membranes makes it impossible to spread out the cross-section of the phloem, in one plane, in such a preparation as that figured. The inner portion of the xylem enclosed by the fibrous sheath/' consists of tolerably wide, elongated prismatic cells, connected without intercellular spaces, with thick almost gelatinously soft mem- branes. Between them are inserted numerous, very narrow, compressed and distorted, spiral and annular tracheides, with thick, distorted, fibrous thickenings; jj>; they doubt- less represent the primitive elements of the bundle. Further outside follow the persistent tracheae, placed
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