STRUCTURE OF CUTICLE I STOMATA. 



421 



analogous to that which occurs in the Palmelleae (§ 317), the outer 

 walls of whose original cells seem to melt-away into the gelatinous 

 investment that surrounds the ' broods ' which have originated in 

 their subdivision. 



313. In nearly all Plants which possess a distinct Cuticle, this 

 is perforated by the minute openings termed Stomata (Figs. 223, 

 224, c, c) ; which are bordered by Cells of a peculiar form, dis- 

 tinct from those of the Cuticle, and more resembling in character 

 those of the tissue beneath. These boundary-cells are usually 

 somewhat kidney-shaped, and lie in pairs (Fig. 226, b, b), with 

 an oval opening 



between them ; but p 29 „ 



by an alteration in a. ' I 



their form, the open- 

 ing may be con- 

 tracted . or nearly 

 closed. In the Cu- 

 ticle of Yucca, how- 

 ever, the opening is 

 bounded by two pairs 

 of cells, and is some- 

 what quadrangular 

 (Fig. 221) ; and a 

 like doubling of 

 the boundary-cells, 

 with a narrower 

 slit between them, 

 is seen in the cuticle 

 of the Indian Com 

 <Fig. 222). In the 

 Stomata of no 

 Phanerogamic Plan t, 

 however, do we meet 

 with any conforma- 

 tion at all to be com 



Portion of the Cuticle of the Leaf of the Iris 

 germanica, torn from its surface, and carrying 

 away with it a portion of the Parenchymatous 

 layer in immediate contact with it : — a, a, elon- 

 gated cells of the cuticle ; b, b, cells of the sto- 

 mata ; c, c, cells of the parenchyma; d, d, impres- 

 sions on the epidermic cells formed by their 

 contact ; e, e, lacunar in the parenchyma, corres- 



pared Yn complexity pouding to the 8tomuta - 

 with that which has 



been described as existing in the humble Marchantia (§ 272). — Stom- 

 ata are usually found most abundantly (and sometimes exclusively) in 

 the Cuticle of the lower surfaces of Leaves, where they open into 

 the. Air-chambers that are left in the Parenchyma which lies next 

 the inferior cuticle ; in Leaves which float on the surface of water, 

 however, they are found in the Cuticle of the upper surface only ; 

 whilst in Leaves that habitually live entirely submerged, as there 

 is no distinct Cuticle, so there are no Stomata. In the erect Leaves 

 of Grasses, the Iris tribe, &c, they are found equally (or nearly so) 

 on both surfaces. As a general fact, they are least numerous in 

 succulent Plants, whose moisture, obtained in a scanty supply, is 



