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Transactions. 



are more numerous, of larger diameter, and more irregular in section. 

 Surrounding the xylem and phloem (between these and the sheath) is 

 small-celled tissue — above the xylem parenchyma, and below the phloem 

 sclerenchyma. 



|i> '%Base of Petiole (fig. 10a). — The epidermis of the upper surface consists 

 of£small cells, usually oval in transverse section, with thin lateral walls 



but thicker internal and external 

 ones. A thin cuticle is present, and 

 there are no stomata. The cells of 

 the lower epidermis are smaller than 

 those of the upper, and have thicker 

 walls. In the upper surface the cells 

 of the layer adjacent to the epi- 

 dermis are large, oval or irregular 

 in shape, with slightly thickened 

 walls. The rest of the ground-tissue 

 consists of large, more or less circular, 

 closely packed cells, many of which 

 contain tannin. Near the lower epi- 

 dermis there is a layer of smaller 

 cells with thickened walls, also con- 

 taining tannin ; the lower epidermal 

 cells contain tannin. The vascular 

 bundles, of which there are three, 

 all large, are of the same structure 

 as in the upper part of the petiole. 

 In this part, however, the cells 

 of the bundle-sheath are suberized. 

 The parenchymatous elements of 

 both xylem and phloem contain 

 tannin. 



Root (fig. 106). — This is a diagram 

 of a section of one of the older roots. 

 On the outside are the remains of 

 the old cortical cells. Then comes 

 a layer of cork-cells, all of which 

 contain tannin, and have thick walls, 

 which are, however, only slightly 

 suberized. Internal to the phellogen is cortex, consisting of irregular cells 

 which have thick cellulose walls, and most of which contain tannin. The 

 pith consists of closely arranged rounded or polygonal cells which have 

 thick walls, and many of which contain tannin. Some of the cells also 

 contain starch, in the form of large rounded grains. The xylem and 

 phloem form a continuous cylinder, the amount of phloem being small. 

 In the xylem the number of vessels is few ; these are oval or circular in 

 section, and thick-walled. The rest of the xylem consists of wood-fibres, 

 which are thick-walled and polygonal in shape, almost free from tannin, 

 but containing a large amount of starch. 



' •* 

 2. Cardamine heterophylla (Forst. f.) 0. E. Schulz var. 



This plant is a slender, almost glabrous herb. Practically all the leaves 

 are radical ; these aie 1-4 in. long, and are imparipinnate, the terminal 

 leaflet being much larger than the others, of which there are usually two 



Fig. 106. — Geum parvijlorum. Transverse 

 section of root ( X 230). a, dead cor- 

 tex ; b, old cork cells ; c, young cork 

 cells ; d, cortex ; c, phloem ; /, xylem ; 

 g, starch-containing cells ; h, pith. 



