Bbtts. — Autecolo^y of Plants of Peridotite Belt, Nelson. 



285 



The spongy tissue is composed of large, irregular, thin-wal ed cells which 

 contain numerous chloroplasts ; there are moderately large air-spaces 

 between the cells. 



In the margins of the leaf the epidermal cells are smaller, and their 

 walls are very much thickened, and Some of them are produced into small 

 papillae. Inside this layer there is a group of small cells which have 

 very thick mucilaginous walls and very small cell-cavities. 



The vascular bundles are small and contain only a small amount of 

 lignified tissue. There is no stereome. The bundle is surrounded by a 

 sheath of thin-walled colourless cells. Below the midrib there are some 

 small, round, thin-walled cells which do not contain chlorophyll: they are 

 for water-storage. 



Peduncle. — The epidermis is composed of small cells which have all 

 their walls, especially the lateral ones, very much thickened. The cavities 

 are small. In addition there is a fairly thick rough cuticle. Stomata 

 are of the same type as in the leaf. 



Fig. 11. — Wahlenbergia albomarginata. Transverse section of leaf (X 48). a, unicellular 

 hair ; b, large cells of upper epidermis ; c, cuticle ; d, stereome in leaf- 



The cortex consists of 3-4 layers of oval cells with slightly thickened 

 walls. These cells are closely arranged so that there are only very small 

 air-spaces ; the cells contain numerous chloroplasts. The endoderinis is 

 well marked, and consists of one layer of cells with thin suberized walls. 



The phloem forms a narrow band. The sieve-tubes are of small diameter, 

 and there is a good deal of parenchyma. 



The amount of xylem is small. There are small groups of vessels 

 surrounded by wood-fibres which have very thick walls and small cavities. 

 The pith-cells are large and round ; most of them are lignified, but there 

 are a few cells in the centre which have unlignified walls. 



Stem (fig. 12). — The epidermis is composed of somewhat larger cells 

 than the epidermis of the peduncle ; in transverse section the cells are 

 squarish ; their lateral walls are only slightly thickened, but the external 



