276 Transactions. 



Art. XXXI. — Notes on the Autecology of certain Plants of the Peridotite 

 Belt, Nelson: Part I — Structure of some of the Plants (No. 3).* 



By M. Winifred Betts, M.Sc. 



[Read before the Otago Institute, 10th December, 1919 ; received by Editor, S^lst December, 



1919 ; issued separately, 30th Jime, 1920.] 



25. Cyathodes acerosa R. Br. 



Habit. — This plant . is an erect, branching shrub, 1-2 ft. high ; the 

 branches are woody and spreading, and the bark is black. The leaves 

 are spreading, ^^ in. long, acerose, linear, rigid, pungent-pointed, glaucous 

 beneath, with 3 to 7 parallel veins. 



Anatomy. 



Leaf. — The upper epidermis is composed of very regular rectangular 

 cells which have the longer sides at right angles to the surface of the 

 leaf. These cells have very thick mucilaginous cell-walls, and their cavities 

 are very small and contain tannin. There is a thick cuticle. 



The lower epidermis consists of small cells which have thick walls (but 

 not nearly as thick as in the upper epidermis).' There is a thick cuticle 

 on this surface also. Most of the cells of the lower epidermis are produced 

 into short papillae with very thick, cutinized walls. Stomata are confined 

 to the lower epidermis ; the guard-cells are small, and are at the same, 

 level as the other epidermal cells. 



The chlorenchyma is differentiated into palisade and spongy tissue. 

 The palisade tissue consists of 3 or 4 rows of narrow, elongated cells. The 

 outermost layer has all the cells full of tannin ; the others contain small 

 chloroplasts. The outer layer is very compact, but there are small inter- 

 cellular air-spaces in the inner layers. 



The spongy tissue occupies about a quarter of the width of the leaf. 

 It is composed of sriiall, irregular, thin- walled cells, many of which contain 

 tannin. There are small intercellular air-spaces in this tissue. 



The number of vascular bundles varies from 3 to 7. The xylem and 

 the phloem are both small in amount, and in the parenchymatous elements 

 there is tannin. Below the phloem there is a mass of stereome, consisting 

 of small cells with their walls so much thickened that their cavities are 

 almost obliterated. Above the upper part of the bundle there is a sheath 

 of small cells with unlignified walls. 



Stem. — The cork forms a narrow band ; it is composed of very small, 

 thick-walled cells which are very closely arranged. 



The cortex consists of oval, thin-walled cells, which contain tannin, 

 and which form a compact tissue with very small intercellular air-spaces. 



The phloem is composed of small elements ; the medullary rays passing 

 through it contain tannin. 



The xylem is composed of a moderate number of vessels which have 

 thick walls. The rest of the xylem consists of wood-fibres which have 

 very thick cell-walls and small lumen. 



*For Nos. 1 and 2 see Trans. N.Z. Inst., vol. 50, pp. 230-43, 1918, and vol. 51, 

 pp. 136-56, 1919. 



