122 



ANATOMY. 



formed of two curbed cells whose concavities face each other. These two small lip- 

 like cells are termed stomata. Stomata, though epidermal organs, differ from the 

 epidermis in that their cells are much smaller, and nearly always situated below 

 those of the epidermis ; they farther present different contents, and especially granules 

 of chloroph3dl ; whence they may be regarded as intermediate between the epidermis 

 and the subjacent parenchyma. 



Stomata are variously distributed over the surface of the leaves : usually solitary, 



often arranged in series, some- 

 times crowded in the base of 

 a cavity (as in some Proteacew, 

 figs. 678, 679). Their number 

 varies : the Iris contains 

 12,000 in a square inch; the 

 Pinlc, 40,000; the Lilac, 

 120,000. When moistened, 

 their lips swell and become 

 more curved, and hence gape ; 

 when dry, they shorten and 

 close. 



Stomata always correspond to intercellular passages, and are found on the 

 ordinary leaves of Phsenogams, principally on their lower surface, on stipules, on 



herbaceous bark, calyces, and ovaries ; 

 they are wanting on roots, rhizomes, non- 

 foliaceous petioles, most petals, and seeds ; 

 acotyledons, and submerged aquatic plants, 

 which have no epidermis, equally want 

 sbomata. 



If a fragment of a stem or leaf be 

 macerated, the cellular tissue beneath 

 the epidermis is rapidly destroyed, and the latter divides into two layers, an 

 external epidermis proper, and a very thin membrane (fig. 680), moulded on the 

 epidermis and extending even over its hairs, which are sheathed in it like fingers in 

 a, glove (p) ; it presents openings (p) corresponding to the stomata. Brongniart has 

 called this membrane the cuticle (little shin) ; it is not cellular, like the epidermis 

 which it covers. 



678. Vertical section of pari of a Banksia 

 leaf (mag.)-' 



679. Part of a Banksia leaf, 

 presenting three sections 

 pai-aUel' to the lower sur- 

 face, and at different 

 depths (mag.)." 



680. Cabbage. Cuticle. 



' Fig. 678 is a section perpendicular to the thickness 

 of the leaf, showing: 1, on the iipper and lower faces 

 two layers of epidermal cells ; 2, fibro-vascular bundles 

 to the right and left, out perpendicularly to their length ; 

 3, on the lower face, a depression, clothed with hairs, 

 and pierced by stomata which communicate with the 

 interstices of a very loose cellular tissue. Above this 

 'tissue, the upper half is a mass of elongated and erect 

 cells, perpendicular to the epidermis. 



' Pig. 679. Three sections parallel to the plane of the 



leaf, carried through three such depressions, each circum- 

 scribed by the fibro-vascular bundles of the nerves. In 

 the cavity at the bottom of the figure, the section has 

 carried away the hairs clothing the walls of the depres- 

 sion, leaving , the stomata and epidermal cells visible ; 

 in the cavity on the right the loose cellular tissue which 

 underlies the stomata of the epidermis is seen through 

 the latter ; in the third depression the section has re- 

 moved all but this subjacent tissue with its intercellular 



