SIZE AND DISTRIBUTION OF STOMATES 



175 



figuration from other cells in the same tissue ; these are called subsidiary cells 

 or accessory cells (Fig. 42, B). In many species of the grass and sedge 

 families the guard cells are distinctly elongate (Fig. 42, C). In most species 

 of conifers, and in certain other species, stomates are of the "sunken" type 



guard 

 ce//s 



^.guard 

 cells 



Fig. 42. Structure of stomates. (/?) surface view of sunflower stomate, (B) sur- 

 face view of Zehrina stomate, showing four subsidiary cells around guard cells, (C) 

 surface view of maize stomate, (D) cross sectional view of Austrian pine stomate. ■ 



(Fig. 42, D). A perspective view of a stomate and the surrounding guard 

 cells is shown in Fig. 43. 



The guard cells differ from the other epidermal cells in that they contain 

 plastids which are green in color. These have often been assumed to be 

 chloroplasts, and are frequently so-called, but the green pigment present does 

 not seem to be true chlorophyll as photosynthesis apparently does not occur 

 in the guard cells. 



Size and Distribution of Stomates. — The size of the stomatal pore 

 varies greatly according to the species of plant, and somewhat even among 



