336 Transactions 



Succeeding leaves show all transitions between simple and 3-foliate, and in 

 certain plants later leaves are still more divided, many being biternate; 

 but this form in Riccarton Bush is always followed by the 3-foliate form 

 of the adult (fig. 6). 



(ii.) Leaf -anatomy. 



(a.) Shade Leaj. — Epidermis : Cells regular and slightly flattened ; outer 

 walls firm, with thin cuticle ; stomata lower surface only, level with epi- 

 dermal surface. Hypoderm : Above midrib 1 layer ; below midrib forms a 

 supporting mass, 4-5 cells in thickness. Chlorenchyma : PaKsade — 3 layers 

 isodiametrical cells rather closely packed ; arm-palisade cells, mentioned 

 by Solereder (1908, p. 15), are numerous in the top layer and are present 

 in smaller numbers in the other layers; wall-infolding is confined to the 

 upper portion of each cell ; chloroplasts irregularly scattered ; tissue com- 

 prises about one-half of leaf-thickness. Spongy- — Cells are more irregular 

 than palisades, but no sharp distinction between the tissues ; intercellular 

 spaces large ; chloroplasts rather numerous. Leaf-margin : Epidermal cells 

 enlarged ; outer walls very convex and much thickened. Vascular bundle : 

 Well-developed parenchymatous sheath. Calcium oxalate : In aggregate 

 crystals. Anthocyan : Sometines in lower epidermis. 



(&.) Sun Leaj. — Epidermis: Cell -walls much thickened, and well- 

 developed cuticle, thicker on upper epidermis. Chlorenchyma : Palisade — 

 Cells more closely packed. Spongy — Intercellular spaces smaller and cells 

 more spherical. Leaf-margin ; Strengthened by 2-3 layers of thick-walled 

 hypoderm cells. Vascular bundle : Sheath more developed. 



(c.) Climhing-organ. — (i.) Form and Behaviour. — The pairs of leaves at 

 first project beyond the growing apex of the stem. The petioles elongate 

 in this position until they attain a length of 3 cm., the leaflets remaining 

 small, being at most 1 cm. in length. The leaves then bend downwards 

 and outwards, the petioles at the same time increasing to 4 cm. in 

 length. When in the horizontal position, the leaf-blades increase in 

 size, and by curvature and torsion of the subpetioles the blades become 

 placed at right angles to the light. If in its downward curvature a 

 leaf-petiole comes into contact with some object the stimulus causes 

 the petiole to coil round the object. The under surface of the petiole 

 is most commonly in contact with the support, but curvature caused 

 by the upper surface of the petiole being sensitive to contact is by no 

 means uncommon. Whether the greater response of the under surface is 

 due to its being more sensitive to contact, or whether it is due to this surface 

 being in a position where it will most often be exposed to stimulation, has 

 not been investigated. But it is obvious that as this results in the leaves 

 being bent downwards it is most suitable in preventing the liane-shoots 

 from slipping down from any support which they have reached. The sub- 

 petioles are quite as sensitive, and it seems that they are equally sensitive 

 on all sides. Like the petioles, they are stimulated to curvature by contact 

 with foreign objects, or with parts of the same plant — stem, leaf, or other 

 petioles. After their contact they become much strengthened, and the 

 portions which are in contact with an object attain a thickness considerably 

 greater than that of the rest of the petioles. The small size of the leaf- 

 blades during the growth of the petioles and subpetioles is of great im- 

 portance in gaining supports, for a large leaf-blade would tend to become 

 entangled in twigs, &c., and by its resistance prohibit a petiole from 

 efficiently coiling round the support. 



