Bird. — Lianes of the Ancient Forest of Canterbury Plains. 323 



extensive flattened masses, but where there is more abundant vegetation 

 it may push its way among the tangled branches and increase the density 

 of these masses. 



It has been stated above that in exposed situations the leaves are 

 reduced to midribs. However, the reduction in this species cannot always 

 be a reaction to environmental factors, for in very damp shady stations 

 certain individuals occur which have their leaves similarly reduced, while 

 adjacent plants show no reduction. Possibly there may be two varieties — . 

 one in which the leaves show reduction in the open only in response to 

 some environmental stimulus, and another in which leaf-reduction is a fixed 

 hereditary character.* 



B. LEAP. 



(ii.) Leaf -anatomy. 



(a.) Shade Leaf. — Leaf 3-5-foliate ; laminae 4-7 cm. long, subcoriaceous, 

 ovate-oblong or ovate-lanceolate, base truncate ; margin deeply serrate. 

 Yellow prickles on under surface of petiole ; few or absent on subpetioles 

 and midribs. 



(&.) Sun Leaf. — Leaf reduced almost to midribs ; terminal 9-12 cm., 

 lateral 7-9 cm. Petiole 6-7 cm. Prickles in large numbers on both petiole 

 and midribs. 



(i.) Leaf -form. 



(a.) Shade Leaf. — Epidermis : Cells almost isodiametrical ; well-deve- 

 loped cuticle ; stomata lower epidermis only. Hypoderm : One layer of 

 thick-walled coUenchyma, extending a short distance from leaf-margins. 

 Chlorenchyma : Palisade — 2 layers cells; upper rather closely packed, 

 second layer looser. Spongy — 4-5 layers irregular cells; intercellular 

 spaces large. Calcium oxalate in aggregate crystals. Vascular bundles 

 surrounded by collenchymatous sheath ; stereome scattered irregularly 

 round the bundles ; on under surface of midribs a strengthening mass of 

 4r-5 layers of coUenchyma. 



(&.) Sun Leaf. — Epidermis : Cuticle very thick ; stomata lower epi- 

 dermis only. Hypoderm : One continuous layer beneath epidermis ; cells 

 large, isodiametrical ; beneath lower epidermis it forms patches of cells 

 beneath the vascular bundles, and extending a short distance on each side. 

 Chlorenchyma : Tissue separated by vascular bundles and their sheaths, 

 which extend from the upper to the lower epidermis. Palisade — Cells 

 elongated and very closely packed. Spongy — Not sharply separated from 

 palisade ; the cells are elongated in the same direction as. the palisade, and 

 intercellular spaces are small. Mechanical tissue is more strongly deve- 

 loped than in shade leaves. Leaf-margin protected by 3-4 layers of coUen- 

 chyma ; chlorenchyma at the margin composed of palisade cells with small 

 ends facing the leaf-surface. 



(c.) Assimilatory Midrib. — Epidermis: Thick walls; outer walls con- 

 vex ; stomata distributed round whole surface. Hypodermis : One layer 

 isodiametrical cells. Chlorenchyma : A continuous ring 2-3 cells thick ; 

 on upper surface cells elongated, forming a palisade tissue ; on under 

 surface irregular cells and intercellular spaces which connect with the 

 stomata through breaks in the hypoderm. Vascular system : A ring of 

 bundles lies close to the chlorenchyma, the dorsal bimdle being greatly 

 enlarged. Medulla composed of large spherical cells with thin walls. 



* For a fuller discussion of this important topic see Cockayne, L., 1901, pp. 291-95. 

 11* 



