STOMATAL GROOVES AND HOLLOWS 



i6i 



the cuticle being relatively thin and the stomata often slightly 

 raised above the general surface (Fig. 8i, C, D).i 



Retarded transpiration is also very effectively attained by 

 restriction of the stomata to grooves or hollows whose commu- 

 nication with the exterior is often partially occluded by an 

 outgrowth of hairs. A good example is furnished by the common 

 Oleander [Nervum oleander). If the lower surface of a leaf of 





_ -^jCDC 



Fig. 82. — Transverse section of part of the leaf of the Oleander {Nerium 

 oleander) showing a stomatal chamber. Col., collecting cells ; 

 e , epidermis ; p., palisade layers ; St., stoma ; V , vascular bundle. 



this plant be examined with a lens, a large number of light- 

 coloured patches appear dotted between the principal veins, 

 each patch being due to a tuft of hairs arising from one of the 

 numerous hollows. In transverse sections (Fig. 82) the latter 

 are seen to extend inwards for slightly more than one-third the 



1 Plugging of the stomatal apertures with particles of wax is observed 

 in some plants (e.g. certain Conifers), which thereby' impede the escape of 

 water-vapour and consequently check transpiration, which is almost 

 entirely cuticular. 



