366 YOUNGKEN— ON THE MYRICACEAE 



Subterranean branch of Myrica Macfarlanei, Youngken 

 The rhizome of the hybrid between M. cerifera and M. Carolinensis 

 shows the following histological peculiarities: — Compared with the aerial 

 stem of the same age, it shows fewer cork layers and a broader cortex. 

 The cells of the cortex are generally larger, less angular, and contain 

 more starch grains. The bast fibres of the phloem are about twice as 

 numerous and in larger groups. The tracheae are fewer and generally 

 broader, while the woody fibres are more numerous and more lignified. 

 The pith is narrower; its elements smaller and more lignified. The pri- 

 mary medullary-rays are broader and frequently show 1-5, less often 1-6, 

 rows of cells in width. The secondary medullary-rays vary in width 

 from 1-2 to 1-3 rows of cells. Cortical parenchyme, phloem, and tracheal 

 elements with a gummy lignin content are more frequent than in the 

 above ground stem. Compared with rhizomes of its parents, it shows 

 intermediate characters in respect to the number and mean diameter 

 of the tracheae and the woody fibres. 



Aerial Stem of Myrica Gale, L 

 (Plate 87. Fig. 23.) 

 In passing from periphery toward the centre, the following histologi- 

 cal peculiarities are seen: — 



1. A cork zone of unevenly stained brick-shaped cells whose walls 

 are partly suberized and partly lignified. The lignification occurs on 

 the inner tangential walls. 



2. A phellogen of thin walled tangentially elongated cells. 



3. A comparatively narrow cortex composed of cells some of which 

 are thick walled and contain gummy lignin, some thin walled, containing 

 starch while others are rich in rosette, monoclinic prism, or crystals and 

 forms of calcium oxalate. The intercellular air-spaces of this region 

 are small to medium and angular. Many contain several crystals of 

 calcium oxalate. The cortex is entirely devoid of sclerenchyme elements. 



4. A pericycle which contains an interrupted zone of sclerenchyme 

 elements. 



5. A very narrow phloem, even in old stems, which is devoid of bast 

 fibres but contains numerous sieve tubes and phloem parenchyme cells. 

 Through this region course numerous medullary-rays which broaden 

 out toward their extremities and arch in many phloem masses. 



6. A cambium of one layer of meristematic cells with thin walls. 



7. A xylem composed of numerous narrow compactly arranged wood 

 wedges separated by medullary-rays which are mostly 1 cell wide (second- 



