Betts. — Rosette 'Plants at Cass. 



273 



Petiole. — -The petiole is very much thickened at the midrib, but is 

 thin at the margin. The upper epidermis consists of fairly large cells, in 

 which the lateral walls are thin, the inner and outer somewhat thickened. 

 Many of these cells are produced into hairs as in the leaf. Stomata are 

 confined to the lower surface. 



The mesophyll consists for the most part of large, thin-walled, rounded 

 or polygonal, closely arranged cells. This tissue is for water-storage. Near 

 the flattened margins of the petiole the cells are smaller and contain a few 

 flattened chloroplasts. 



Fig. 33. — Gnaphalium Traversii. Transverse section of leaf, passing through midrib 

 (X 175). a, palisade tissue; 6, spongy tissue; c, two-celled hair; d, stoma; 

 e, glandular hair ; /, xylem ; r/, phloem ; h, aqueous tissue. 



There are three vascular bundles, the one in the midrib being large, 

 the others smaller. Each is surrounded by a small amount of thin-walled, 

 colourless parenchyma ; the bundle has the same structure as in the leaf. 



Runner (fig. 34). — This is cylindrical in transverse section. The 

 epidermis. consists of small cells, much smaller than in the petiole, which 

 have all their walls slightly thickened. Some of these cells are produced 

 into hairs like those in the leaf, except that, while in the leaf they are 

 usually two-celled, in this case they are three-celled. 



