CHAPTER II. PLANT TISSUES. 



157 



they thus serve to control the amount of evaporation from the 

 plant. 



Water-pores are also openings in the epidermis, bearing some 

 resemblance to stomata, but differing from them in the fact that 

 the guard-cells are immovable, and the opening, therefore, does 



Fig. 408. — Small portion of transverse section of Tulip leaf, giving sectional view of one 

 of the stomata. g, one of the guard-cells; /', large intercellular space beneath stoma. 

 Magnified 480 diameters. 



not increase or diminish, and also in the fact that water, instead 

 of gaseous matter, commonly fills the orifice or oozes out upon 

 the surface. Their distribution is also different from stomata. 

 While the latter are most abundant between the veins on the 



under surface of leaves, water-pores 

 occur at the extremities of veins on 

 the margin of the leaf and usually 

 toward the upper side. Fig. 409. 



Fig. 409. Fig. 410. 



Fig. 409. — Section of leaf of a species of Saxifrage, showing two water-pores at ths 

 extremity of a vein. Above them are two hairs, to which usually a deposit of calcium 

 carbonate clings, on evaporation of the water excreted by the pores. Modified from Vines. 

 Magnified about 50 diameters. 



Fig. 410.- Section of branch of Currant, showing cork cells, and the way they ar- 

 formed. c, chlorophyll-bearing parenchyma : /', cork-cambium; a, mature cork cells. 

 Magnified about 275 diameters. 



