294 Transactions. 



Stem (figs. 20 and 21). — The general arrangement of the tissues is shown 

 diagrammatically in fig. 20. From this it will be seen that the stem is 

 tetragonous and that in each of the corners there is a small mass o^ scleren- 

 chyma. The structure of the stem is shown in detail in fig. 21. 



On the outside there are dead epidermal cells with a thin cuticle, and 

 below this there are a few dead cortical cells. Beneath this layer there are 

 2-4 layers of large, squarish cells which have their cell-walls both suberized 

 and lignified. The portion of the cell-wall adjacent to the cell-cavity is 

 suberized, and nearer the middle lamella it is lignified. 



Inside this corky layer there is a zone of cortex. The cells of this tissue 

 are more or less oval in transverse section, and are closely packed together 

 so that the intercellular air-spaces are very small. These cells contain a 

 small number of chloroplasts. At intervals there are groups of pericycle 

 fibres. These are of small diameter and have thick walls. In the four 

 corners of the stem there is a mass of sclerenchyma, which is composed of 

 slightly larger cells than the pericycle fibres. 



The phloem forms a continuous band with its elements rather regularly 

 arranged. The xylem is composed for the greater part of wood-fibres 

 which have thickened walls. 



The medullary rays are not numerous ; they are multiseriate (3 cells 

 wide), and their cells have thickened, lignified walls. 



The pith is composed of large round or polygonal cells, which have 

 lignified, somewhat thickened, cell-walls. 



32. Helichfysum bellidioides Hook. f. 



Habit. — -This plant is an herb. The stems are prostrate, slender, much 

 branched, almost woody at the base, 6-12 in. long ; the branches are 

 numerous, erect, and leafy. The leaves are loosely imbricating, spreading, 

 ^\ in. long, obovate-spathulate, apiculate, flat, one-nerved, with the upper 

 surface glabrous and the lower clothed with cottony tomentum. 



Anatomy. 



Leaf. — The upper epidermis consists of regular, large cells, which have 

 their inner and lateral walls thin and the external ones slightly thickened. 

 There is a thin cuticle. A few of the cells are produced into hairs. 



The lower epidermis consists of cells that are smaller than those of the 

 upper epidermis. Their walls are thin, and there is a very thin cuticle. 

 Many of these cells are produced into fine 2- or 3-celled hairs, which form 

 a dense tomentum on the under-surface. 



The chlorenchyma is differentiated into palisade and spongy tissue. ■ 

 The palisade tissue consists of 2 rows of cells with thin walls and numerous 

 large chloroplasts ; there are air-spaces between the cells. 



The spongy tissue is composed of large, irregular, thin-walled cells, 

 which contain abundant large chloroplasts. These cells form a rather 

 loose tissue with large intercellular air-spaces. 



Stomata are confined to the lower epidermis, and the guard-ceUs 

 are raised (as in Celmisia longifolia var. gracilenta, Olearia virgata, and 

 0. arborescens). The guard-cells are small. 



The vascular bundle is small, and is surrounded by a sheath of thin- 

 walled cells which contain a very few chloroplasts. Just above the xylem 

 there is a small group of 8 or 10 sclerized cells. The amount of lignified 

 tissue in the xylem is small ; both xylem and phloem contain parenchyma. 



