382 YOUNGKEN— ON THE MYRICACEAE 



cuticle of this epidermis is somewhat thicker than that of the lower 

 epidermis. Many of the epidermal elements contain brownish contents. 

 In some the contents appear granular. Numerous bases of sclerotic 

 unicellular hairs are scattered here and there over the surface. A few 

 sclerotic hairs are found and generally occur above the mid-rib and the 

 veins. Each of these is somewhat elevated and surrounded by usually 

 radially arranged cells. Crypts, containing stalked yellowish glandular 

 hairs are numerous. These are generally deeper than those of the lower 

 epidermis. The mesophyll shows a differentiation into a broad upper 

 paHsade zone, a middle spongy parenchyme region and a narrow lower 

 palisade layer. The upper palisade zone consists of three layers of colum- 

 nar shaped cells with variously stained contents. Some of them con- 

 tain crystals of calcium oxalate which may be in the form of rosettes, 

 monoclinic prisms or crystal sand. Others contain one to several 

 radiating structures which suggest the Actinomyces rosette. The spongy 

 parenchyme region is composed of small celled elements which are ir- 

 regularly shaped and surround intercellular air spaces. The lower 

 paHsade layer is incompletely differentiated and consists of columnar 

 as well as irregular shaped cells, which are loosely arranged. Some of 

 these contain crystals of calcium oxalate. The fibrovascular bundles 

 of the mid-rib and veins run through the spongy parenchyma zone. 

 Those of the stronger veins, as well as that of the mid-rib, are connected 

 with both lower and upper epidermis by hypodermal elements. Those 

 above the bundles are usually lignified. Many of the non-lignified 

 hypodermal elements contain rosettes of calcium oxalate. The vascular 

 bundle of the smaller veins is connected with both iht upper and lower 

 epidermis by special layers of elongated cells with wide lumina. The 

 lower epidermis is less cutinized than the upper and consists of cells 

 which for the most part have their outer walls arched in papillose fashion 

 giving to this epidermis a roughened aspect. Numerous crypts contain- 

 ing yellow stalked balloon-shaped glandular trichomes are found, but 

 these appear broader and shallower than those of the upper epidermis. 

 Stomata are also present but more numerous than on the upper surface. 

 They are covered in by neighboring cells. The yellow balloon-shaped 

 trichomes consist of a stalk or pedicel supporting a balloon-shaped 

 head. The stalk is usually 3 cells high, the basal layer alone consisting 

 of 2 cells. The head or gland contains oil which resinifies as the leaf 

 ages. Simple unicellular sclerotic trichomes as well as the bases of 

 these are also found, but in larger numbers than on the upper epidermis. 

 Occasionally a 3-4 celled uniseriate glandular hair is found which has 



