Caryophyllaceæ. 273 



regards the number of stomata per unit of surface the 

 reader may be referred, for instance, to Børgesen. 



The apertures of the stomata, at all events in the narrow- 

 leaved species, lie parallel with the longitudinal axis of 

 the leaf. 



That the guard-cells are surrounded by the other epi- 

 dermal cells in a peculiar manner, was, as far as 1 know, 

 first pointed out and figured by Vesque (Anm. sc. nat., 

 1883, 6. Sér., 15, p. 130): "Les stomates sont embrassés 

 par deux cellules dont la cloison séparatrice et perpendi- 

 culaire à l'ostiole". See the preceding Fig. 14, E and F\ 15, 

 E and F; 16, H and /; 17, J; 19, D; 20, F; and Fig. 21, 

 J and L, all of which, in addition, show, here and there, 

 a small deviation of minor importance, in that an a])erture 

 may be surrounded by 3 — 4 cells, but each end of the stoma 

 is always limited by a more or less crescent-shaped cell. 



Hairs are found in many of the species, in some even 

 in such great numbers, that they become quite pilose, 

 this is especially the case in Cerastium alpinum, which is 

 otherwise exceedingly variable as regards the extent to 

 which it is hairy. The hairs are of two kinds, both consisting 

 of a single row of cells arising from a single epidermal 

 cell, as already pointed out by Vesque (1883). The one 

 kind of hair is thick-walled and dead (filled with air), and 

 terminate in a point (Fig. 15, D and Fig. 17, F); they are 

 specially numerous in the form lanata of Cerastium alpinum. 

 Their function must be to protect the plant against exces- 

 sive transpiration. The other kind of hair is secretory, and 

 its terminal cell is globular (see for instance Minuartia verna, 

 Fig. 18, C, and Cerastium alpinum, Fig. 17, i/ and A). 



The Vascular bundles. It is, at all events in the 

 narrow-leaved species, only a single bundle, which from the 

 stem enters into the leaf, and there quickly develops a 



