430 



.V. F.. Stevens— New Jersey Palmoxylon. 



The outer cortex consists of from six to ten layers of 

 elongated, lignified cells with very thick walls and small lumen. 

 The outer zone of the inner cortex is also composed of lignified 

 cells, but they are thinner-walled and shorter in proportion to 

 their length. The cells of this region differ considerably in 

 size, the outermost cells having about the same diameter as 

 the adjacent cells of the outer cortex, while to'ward the center 

 the cells become progressively larger in diameter. 



The middle zone of the inner cortex contains numerous 

 large air spaces. These air spaces (lacunae) are radially 

 arranged, six to ten times as long as broad, with from one to 



Fig. 15. 



















ffiB? 





Fig. 15. Photomicrograph of cross section of palm root, showing cortex 

 with large radial intercellular spaces in the middle zone ; and stele with 

 alternate phloem and protoxylem groups and eight internal vessels, x 8. 



six layers of cells separating them. The cells of this region 

 are only about twice as long as they are broad and much thin- 

 ner-walled than those of the outer region. In addition to the 

 large radial air spaces, triangular spaces show plainly in the 

 longitudinal section at the intersection of cell walls (fig. 16). 

 The cells are apparently " lignified parenchyma." 



There occur also in this middle zone thick-walled cells with 

 large cavity and large pits. These usually occur singly or 

 scattered through the middle zone in groups of two or three, 

 but are somewhat more numerous toward the inside. Seen in 

 cross section, figs. 13 and 14, they usually appear rather 

 round ; and in fully developed roots the pits are not usually 

 seen in cross sections. In smaller roots, however (fig. 22), the 

 large pits are very evident. Figure 17 shows two of these 



