Betts. — Rosette Plants at Cass. 257 



of several kinds (figs. 5-8). There are on both surfaces of the leaf long, 

 stifi, bristly, unicellular hairs, which are prolongations of epidermal cells 

 and which have thick walls. Hairs of this type are scattered over the upper 

 surface of the leaf, also on the petiole, and on the lower surface of the leaf 

 they arise from the epidermal cells in the vicinity of the vascular bundles 

 (fig. 6). The epidermal cells round many of these are somewhat larger 

 than the others, forming a kind of cushion round the base of the hair 

 (figs. 5 and 8). In addition to the above-described unicellular hairs, there 

 are much shorter, thinner unicellular hairs, both on the leaf (especially 

 the lower surface) and the petiole (figs. 3, 6, 10). Hairs of a third kind 

 (figs. 6 and 7) are found near the vascular bundles on the lower surface of 

 the leaf : these are club-shaped, multicellular, glandular hairs ; they consist 

 of 3 or 4 cells, of which the basal cell is thick-walled and contains only a 

 small amount of .protoplasm ; the other 2-3 are thin-walled and filled with 

 granular protoplasm. The end cell is much larger than the others. 



The chlorenchyma (figs. 3 and 4) is differentiated into palisade and 

 spongy tissue. The former consists of two layers of cells which are fairly 

 compactly arranged ; the spongy tissue is nearly twice as wide as^ the 

 palisade, and is compbsed of rounded or irregular cells with larger air-spaces 

 between them. In both the cell- walls are slightly thickened, and there are 

 numerous large oval chloroplasts. 



In the midrib (fig. 3) there are usually three vascular bundles, of which 

 the central one is the largest. Each vascular bundle is surrounded by a 

 small amount (a layer about 3 cells deep) of colourless parenchyma. 

 Practically the whole of the midrib is filled with an aqueous tissue consisting 

 of large cells with slightly thickened walls ; these cells are circular in trans- 

 verse section and are closely arranged. Just above the vascular bundle 

 some of these cells contain a few chloroplasts. In the midrib, the lower 

 epidermis consists of cells which are small, thick-walled, and, in transverse 

 section, circular. The cuticle here is somewhat thicker. The layer of cells 

 next to this epidermis has thicker walls than the rest of the aqueous tissue, 

 and the cells themselves are smaller. The xylem consists of vessels which 

 are circular in section, of small diameter, and with thick walls ; with the 

 vessels there is xylem parenchyma ; the phloem is composed of sieve- 

 tubes, companion cells, and a little parenchyma. Below the phloem there 

 is a small mass of sclerenchyma. 



Petiole (fig. 9). — This diagram is of half the petiole. The epidermis 

 consists of very small cells in which all the walls are thickened, especially 

 the internal and external walls ; a cuticle somewhat thicker than that in 

 the leaf is present. Stomata are found on both surfaces. Some of the 

 epidermal cells are produced into the two kinds of hairs described in 

 connection with the leaf. The short hairs are much more numerous than 

 the long ones. Practically the whole of the ground-tissue forms an aqueous 

 tissue in which the cells are large, rounded or polygonal, with slightly 

 thickened cellulose walls, and are closely arranged so that there are only 

 minute air-spaces between the cells. The three layers of cells just inside 

 the epidermis are smaller, and have thicker walls ; in these cells there are 

 a few chloroplasts. 



The vascular bundles are arranged in the form of a crescent, ^the largest 

 being at the centre. Each vascular bundle is surrounded by a sheath of 

 cells, which is clearly distinguished owing to the fact that the cells contain 

 tannin. Round the sheath the cells of the ground-tissue are much smaller. 

 The vascular bundles are the same as in the leaf, except that wood-vessels 

 9— Trans. 



