386 



(Fig. 32, В^ С]. The st om ata are either on a level with the 

 surface or project slightly. Børgesen and Wagner record the 

 number to be equal upon both surfaces, Resvoll records 44 

 per sq. mm. upon the upper as against 62 per sq. mm. upon the 

 lower surface. Chlorophyll is present in the epidermis. From 

 one to two layers of palisade-cells occur which are scarcely 

 twice as high as they are broad and are somewhat barrel-shaped ; 



Fig. 32. Й. pygmæris. 



A, Transverse section of leaf (Danmarks Ö; ^w/i). B, Epidermis of the upper surface of 

 the leaf (ibid; ""/i). C, Epidermi.4 of the lower surface of the leaf (ibid; ""/i). D, Sur- 

 face section of palisade-layers (ibid.; "'Vi). E, Surface section of spongy parenchyma 

 (ibid.; ^'"/i). F, Transverse section of leaf-stalk (^^/i). 



they constitute from ^h to Vi of the thickness of the mesophyll. 

 The spongy parenchyma consists of branched cells and is 

 very loose in structure especially in its lower part where large 

 slit-like lacunae are often seen between the subepidermal layer 

 and the rest of the mesophyll; (Fig. 32, A,D,E). The bundles 

 are not accompanied by stereom and are surrounded by a sheath 

 containing chlorophyll. 



Each leaf-apex terminates in an epithema the structure 



