STOMATA. 



29 



and their appendages. They are, however, also met with on parts 

 not green, as on coloured sepals or petals, as those of the Marsh Mari- 

 gold and Ornithogalum. They have also been seen on internal organs, 

 as the replum of some cruciferous plants. They are not usually found in 



.p e •;b 



Fig. 77. 



Fig. 78.' 



cellular plants, nor in plants always submerged, nor in pale parasites. 

 This is not, however, a universal rule, for stomata have been detected 

 in Marchantia and some other Oellulares ; also in the submerged leaves 

 of Eriocaulon setaceum,-and in the pale parasite Orobanche Ei;yngii. 

 They do not exist on roots, nor in plants kept long in darkness so as 

 to be blanched or etiolated, and they are rare or imperfectly developed 

 in succulent plants. 



Stomata vary in their form. s 



The oval form is very common, 

 and may be easily seen in Lilia- 

 ceous plants ; the spherical occurs 

 in Oncidium altissimum and the 

 Primrose, the quadrangular in 

 Yucca and Agave. In the Ole- 

 ander, in connection with the sto- 

 mata, there are cavities in the epi- 

 dermis protected by hairs (fig,79s). 



The development, of stomata has been traced by Mirbel and Mohl. 

 In the Hyacinthus orientalis, they appear first between the epidermal 

 cells in the form of quadrangular spaces containing granular matter, 

 which gradually collects towards the centre of the space, where a sep- 



Fig. 77. Vertical section of epidermis, from the lower surface of the leaf of Madder, 

 Bhcvying the intimate union of the epidermal cells, e e, the loose subjacent parenchyma, p, 

 with intercellular canals, m, and lacuna, I. s. Stoma. Fig. 78. Epidermis of leaf of Saxi- 

 fraga sarmentosa, showing clusters of stomata, s s, surrounded by large epidermal oeUs, e e. 

 The cells among which the stomata occur are very small. Fig. 79. Vertical section of 



lower epidermis of the leaf of JVemtm Olea/nder. e, Epidermis composed of several layers 

 of cells, p, Parenchyma of the leaf, s. Cavity filled with hairs, at the bottom of which is 

 a stoma. 



Fig. 79. 



