STRUCTURE. 



45 



such cells, with occasionally a small intercellular space, and here and 

 there a typical stellate cell many times as large as the cortical cells. 

 In N. lotus the exo-cortex is 23 or 24 cells thick ; each cell is ellipsoidal, 

 the radial axis (with regard to the stem) being shortest, and the horizontal 

 tangential axis longest. The walls appear thickened, and probably are 

 colloid. There are no starch grains, no intercellular spaces and no 

 stellate cells. 



The relative amount of lacunar cortex is very different in the different 

 types of stem. In the Castalia group it is quite prominent (Fig. 16), in 

 the others rather insignificant ; the following table shows the relation in 

 five types examined. " Central core " includes endo-cortex and all within it. 



In N. lotus (cf. Fig. 18 ;) the lacunar cortex might be said to occur in 

 isolated patches of irregular shape around the periphery of the stem. 

 The greater part of these regions is air space, and this is traversed in 

 every direction by anastomosing chains of cells, after the manner of a 

 loose, spongy parenchyma of a leaf. The cells are thin-walled, small, and 

 nearly isodiametric in N. odorata and alba candidissima, and the chains 

 may consist of one or more rows of these (Fig. 17), being sometimes 

 rather plate-like ; the nodes of the network are always multicellular. In 

 N. lotus, on the contrary, the cells are three to four times longer than 

 broad, or they may have a rounded body with slender arms reaching out 

 to connect with neighboring cells. 



The inner cortex and the tissue forming the groundwork of the 

 central core of the stem alike consist of medium-sized spherical cells, 

 containing numerous starch grains, and enclosing large intercellular 

 spaces. There are about 25 cells radially outside the vascular region in 

 N. alba candidissima, constituting the endo-cortex. In N. lotus the endo- 

 cortex may be 0.4 cm. deep in a large stem, and consists of very many 

 cell layers. The cells are wide apart, reaching out toward each other by 

 short, narrow processes, and are surrounded by a large amount of air 

 space ; the tissue is of a whitish color. The cells and spaces are smaller, 

 but otherwise it does not differ from parts of the brown medio-cortex. 



