Finlayson. — Stem-structure of Leafless Plants. 36^, 



Discaria toumatou, Eaoul. 



This plant belongs to the order Bhamnacece. According 

 to Hooker, :;: its habitat is " east coast and interior of the 

 southern part of the North and throughout the South Island" 

 (p. 44). He describes it as "a thorny bush in dry places, 

 becoming a small tree in damper localities, with spreading 

 branches, and branchlets reduced to spines 1 in. -2 in. long. 

 The leaves are small, being fin. -fin. in length, fascicled in 

 the axils of the spines, and absent in old plants." This plant 

 can hardly be described as leafless ; it forms a connecting- 

 link between the plants with abundant leaves and those which 

 are quite leafless. 



The spines borne on the smaller branches are really modi- 

 fied shoots ; they arise decussately in the axils of minute 

 scales ; the length of the branch between each pair of spines 

 is about 1 in. (fig. 1). They occur with great regularity as a 

 rule, but in favourable situations they may be almost entirely 

 suppressed, and are then represented only by aborted bud- 

 shoots appearing as little warts on surface of the stem. In 

 spring, below each spine arise three or four leaves, together 

 with three or four small sessile flowers ; these arise not from 

 the spine, but from the stem immediately below the spine. 

 No bud of leaves covers the branch-termination. Both spines 

 and younger stems are green. 



Leaf -structure. 



The leaf is of the ordinary dorsiventral type (figs, lb, lc). 

 In the centre is the midrib with lateral veins. On the upper 

 surface is an uninterrupted layer of large epidermal cells, 

 appearing squarish in transverse section, with a very thin 

 cuticular layer on the outside wall. Underneath are about 

 three layers of small -celled closely packed palisade cells, 

 which pass over into the more spongy tissue of the lower 

 surface. A single epidermal layer, whose cells are rather 

 smaller than those of the epidermis of the upper surface, 

 with numerous stomata (figs. 2a, 2b, 2c) whose opening is 

 best seen in a longitudinal section of the leaf (fig. 2c), 

 bounds the under-surface of the leaf. Its outer walls are 

 also slightly cuticularised. 



In the centre of the leaf is the midrib, with xylem above 

 and phloem below. Between the phloem and the lower epi- 

 dermis are transparent protoplasmic rounded cells, which 

 probably contain water. There are no hairs present on upper 

 or lower surface. 



* " Handbook of the New Zealand Flora," by J. D. Hooker. Lon- 

 don : Reeve and Co., Covent Garden, 1867. 



