ANATOMY OF CHLORIS PETRAEA. 



291 



Pig. 38.— Ckloris petraea— ventral portion of leaf blade. 

 Transverse section, showing epidermis (Ep) and 

 subepidermal stereome (St); at M the mestonie 

 sheath of a bundle, bordering on layers of colorless 

 parenchyma. Scale J240. 



dry, strongly keeled on the dorsal face and slightly impressed ven- 

 trally opposite the midvein, with a large mestome bundle at the apex 

 of and 3 smaller ones on each side of the keel. Hairs none. 



Epidermis: Ventral, differentiated as bulliform cells in a rather 

 wide band above the keel and 



in 2 small groups of about, 4 ..-• '**-v. v 



cells each, 1 between the first 

 pair of nerves on each side of 

 the keel; elsewhere pi u rice 1 hi- 

 lar (3 or 4 layers) and occu- 

 pying more than one-half of 

 the thickness of the leaf, ex- 

 cept above the larger nerves, 

 thin- walled (except the outer 

 wall of the outermost layer) 

 and large (except the single 

 outermost layer where it lies 

 above the subepidermal groups of stereome); stomata none. Dorsal 

 epidermis one-layered, with cells all small, the outer wall and cuticle 

 much thickened, radial walls thin, undulate, one row of short cells 

 with strongly silicified walls alternating with several rows of long ones, 

 many of the cells developed into rounded, not silicified, papillae; 



stomata in the strips of epi- 

 dermis which lie between 

 the nerves, level with the 

 epidermal surface. 



Subepidermal stereome 

 (fig. 38) in flattened sup- 

 ports above and below the 

 mestonie bundles, that on 

 the ventral side in 1 or 2 

 layers above the larger 

 nerves, reduced to small 

 groups (sometimes only 2 

 cells) above the smaller 

 ones; on the dorsal side 

 supports stronger, some- 

 times 3-layered; also in 

 the leaf margins. 



Chlorenchyma, pal isade, 

 arranged radially in a sin- 

 gle row of cells on each 

 side of each mestonie bundle, with a "bridge" of small-celled chlo- 

 renchyma, containing usually a few cells of colorless parenchyma, 

 connecting each 2 neighboring rows; chlorophyll likewise in Ihe 

 parenchyma sheath where it adjoins the palisade. 



Fig. 39. -Chlor is petraea large mestome bundle from loaf 

 blade. St, stereome of lower face of blade, bordering on 

 the mestome sheath (M), which encircles both the lep- 

 tomo and hadrome as a closed sheath of thick- walled, 

 porous cells. Bordering on the mestome sheath is a 

 green parenchyma sheath (P). VV, vessels; L, laouno 

 with an annular vessel. Scale 560. 



