350 YOUNGKEN— ON THE MYRICACEAE 



1. Epidermis of polygonal cells highly cutinized on their outer face 

 and giving rise to short and long, frequently bent, unicellular trichomes 

 and short stalked glandular trichomes with balloon-shaped heads (M. 

 Carolinensis and M. Macfarlanei) and both bowl- and balloon-shaped 

 heads {M. cerifera). 



2. Cortex of 6-8 layers of radially arranged polygonal cells, larger in 

 the meso- and endo- than in the exocortex region. Many of these cells 

 contain tannin, some starch grains, others rosette and monoclinic crys- 

 tals, a few gummy lignin. 



3. Endodermis not distinguishable from the other cells of the endo- 

 cortex. 



4. Pericambium showing a discontinuous ring of sclerenchyma ele- 

 ments. 



5. Open collateral fib ro- vascular bundles whose phloem region is 

 very narrow and composed mostly of sieve tubes and phloem cells. The 

 phloem cells are loaded with tannin. 



6. A rectangular pith zone of polyhedral parenchyma cells whose 

 walls are thickened. Many of these cells contain starch and a few gummy 

 hgnin. 



First pair of fohage leaves of M. cerifera 



The upper epidermis is composed of cells with slightly wavy vertical 

 walls having a thicker cuticle than those of the lower epidermis and 

 showing no stomata. In surface view these cells have a mean measure- 

 ment of 33.99 M X 26.22 m. 



The cells of the lower epidermis have more prominently wavy vertical 

 walls with a mean measurement of 36.42 /x X 24.28 fx. The cells over the 

 veins possess rectilinear walls and are somewhat elongated. Among 

 the lower epidermal cells are to be noted many stomata which are slightly 

 elevated and surrounded by 3-8 neighboring cells. 



The mesophyll shows dorso-ventral differentiation into palisade and 

 spongy parenchyma regions. The palisade zone consists of two layers. 

 The upper one of distinctly columnar shaped cells, the lower of both 

 columnar and cuboidal cells which for the most part are more loosely 

 arranged and smaller than those of the upper layer. The spongy paren- 

 chyma region consists of small rounded to irregular shaped cells which 

 surround large intercellular air spaces. A few of these cells are filled 

 with gummy lignin, probably due to the invasion of the endophyte which 

 will be discussed later. 



The mid rib and lateral veins are found coursing through this region. 

 The mid rib shows 1 or 2 layers of schlerenchyma elements bordering its 



