76 



A. H. Graves, 



Figure 3. — Longitudinal 

 section of a portion of 

 corticai parenchyma cells, 

 showing undulations in 



tlie side walls, x 210. 



rounded so that intercellular spaces often occur, and elongated in the 

 direction of the length of the stem (PI. I, fig. 5 ; PI. Ill, fig. 7 ; Text-fig. 3j. 

 The majority of the cortical parenchyma cells show in an oblique 

 view parallel horizontal stripes or bands on their side walls. A lon- 

 gitudinal section proves that this appearance is due not to bands of 

 thickening, but to slight undulations (Text-fig. 3). These are not 



necessarily regular in size or distance 

 apart; they may or may not occur all 

 through the cell, and certain cells are 

 apparently entirely without them. Their 

 function is not clear. Similar undulations 

 were observed by Caspary (1858) in sev- 

 eral aquatic plants, notably in Zannichellia 

 palustris. Prillieux (1864) has also noted 

 them in the stem of Althenia filiformis 

 and in the roots of epiphytic orchids. 

 Another point of general interest in the 

 stem cortex is the occurrence of starch 

 grains. These, as shown in PI. I, fig. 5, 

 are quite numerous. Their size evidently 

 increases in the vicinity of the axial and cortical bundles and every- 

 where at the nodes. Irmisch (1858, p. 35) has found starch abundant 

 in the Potamogetons and has described its occurrence and appear- 

 ance in considerable detail. 



In the cortex appear also the secretion cells noted in the epi- 

 dermis, that is, they are apparently of the same nature, behaving 

 in general in a similar way. They do not contain starch, as do 

 most of the cortical cells, but are filled with fine granular contents 

 and are especially abundant at the nodes. Bomet (1864, pp. 40—41) 

 has noted cells evidently quite similar in the cortex and vascular 

 tissue of Cymodocea, filled with a " liquide oleagineux, un peu teinte 

 de jaune, tout-a-fait semblable a celui que renferment les cellules 

 epidermiques des antheres." 



In describing the cortex we may for convenience divide it into 

 three portions : (a) an outer zone of cells, compactly arranged and 

 bounded on the outside by the epidermis ; (b) a central area, with 

 a large portion of its territory occupied by a ring of lacunae or 

 air spaces; and (c) an interior zone of cells limited on the inner 

 side by the endodermis (PI. I, fig. 5). 

 (a) Outer cortex. 



The outer portion of the cortex consists of two or three layers 

 of cells (PI. I, fig. 5 oc; PL III, fig. 7). The cells of the outermost 



