Betts. — Aut ecology of Plants of Peridotite Belt, Nelson. 2-Ao 



Anatomy. 



Leaf. — Both the upper and the lower epidermis consist of small cells 

 which in transverse section are oblong. The cell-walls are thin, but the 

 lateral and external walls are cutinized. The cuticle is smooth and fairly 

 thick. Stoma tes are confined to the lower surface. The guard-cells are 

 at the same level as the other epidermal cells, and the stoma is protected 

 by guard-cell ridges. 



Below the upper epidermis there is a hypoderma composed of 2 rows 

 of large cells with thick walls. These cells contain tannin. Above the 

 lower epidermis there are 1-2 broken layers of kypodermal cells; these 

 in transverse section are more or less rounded, have thick walls, and contain 

 tannin. 



The chlorenchyma is differentiated. The palisade tissue consists of 

 3 rows of cells with thin walls and numerous chloroplasts. The two 'outer 

 layers are very compact, but the third layer has fairly large air-spaces 

 between the cells. The spongy tissue consists of irregular thin-walled cells 

 with abundant chloroplasts. These cells are loosely arranged, so that there 

 are large intercellular air-spaces. 



The midrib is prominent. Above and below it the epidermal cells are 

 smaller and the hypoderma is thickened. On the lower surface there is 

 collenchyma. Below the hypoderma there are a few small cells, which 

 contain chloroplasts. The vascular bundle forms an irregular cylinder, in 

 the centre of which there are round cells with lignified walls. The xylem 

 consists of vessels of small diameter and of wood-fibres. The phloem is a 

 narrow zone formed of small cells. Outside the phloem there is a narrow 

 band of small sclerenchymatous cells with thickened walls. 



Stem. — The cork is a wide band of tissue in which the cells are large 

 and irregular. The phellogen is well marked. 



The cortex consists of oval cells with thick walls. These cells contain 

 abundant starch-grains, and are compactly arranged, so that there are only 

 small intercellular air-spaces. 



The pericycle fibres form a continuous band around the phloem. These 

 fibres vary considerably in diameter, and have their walls very much 

 thickened, so that the lumen is small. 



The phloem forms a fairly wide band with numerous uniseriate medullary 

 rays which contain tannin passing through it. The xylem is well developed, 

 and is composed of vessels of fairly large diameter and of wood-fibres with 

 thick walls and small cell-cavities. 



The medullary rays are numerous and are uniseriate, and have thickened 

 lignified walls, except in the phloem, where the walls are not lignified. The 

 pith is solid and consists of roundish cells with thickened lignified walls. 

 The cells contain abundant starch-grains and are closely packed together, 

 so that there are only very small intercellular air-spaces. 



