M'CRONE: HISTOLOGY OF MALVA. 265 



form seven shallow lobes, and through the middle of each lobe 

 runs one large vein from which all of the veins branch to form 

 a more or less close network of small veins. 



The leaf is dorsiventral, with palisade tissue on the upper 

 side only. The palisade cells (figs. 8, c, 9, c, 10, a) are usu- 

 ally closely packed together, with rather large air chambers 

 beneath the stomata (fig. 10, c and d, and figs. 5 and 6) which 

 connect with the numerous air spaces between the cells of the 

 spongy parenchyma. 



The surfaces of the leaf, both upper and lower, are covered 

 thickly with hairs of three different kinds. The most numer- 

 ous of these are stellate hairs having from five to nine rays 

 (fig. 4). There are more hairs to the square millimeter on 

 the young leaf than on the fully developed one. The average 

 number of hairs on the young leaf is 36 to the square milli- 

 meter. This is just after the leaf has unfolded. A gradual 

 decrease in number was found in leaves of successive ages, 

 fully developed leaves having 13 to the square millimeter. Be- 

 side the stellate hairs, along the veins and along the margin of 

 the leaf, are numerous one-celled hairs about the same in 

 structure as one ray of the stellate hair. The surface of the 

 hair is smooth. The center stains darker than the wall, giv- 

 ing the appearance of a core. The cells from which these 

 hairs arise form a slightly raised papilla, while the stellate 

 hairs are on a considerably raised papilla. The third kind 

 mentioned are glandular hairs (fig. 8, /). These are many- 

 celled hairs and are generally found at the veins. They are 

 the same in structure as those found on the petiole and young 

 parts of the stem. The nucleus in the cells of these hairs is 

 always clearly visible. 



The cells of the epidermis, are very irregular in size and 

 shape and the walls are thin (fig. 13). Waterproofing is fur- 

 nished by a thin cuticle merely. Many of the epidermal cells 

 are mucilagenous (fig. 13, e). Whether this mucilage is a 

 modification of the cell wall or not has been discussed by 

 Kuntze (1891). He describes the mucilage of the epidermis, 

 which is characteristic of the mallow family, as being a modi- 

 fication of the cell wall. He quotes Dumont as believing that 

 in some species at least the mucilage has a schizogenous origin. 

 It is certain that young cells are sometimes stratified. In older 

 tissue the walls appear to entirely dissolve and leave the muci- 



