ANATOMY OF mrgai.odonta brckii 339 



to light. The section shown was made somewhat obliquely through 

 the organ, showing several layers of cells of the tissue connecting 

 the outer lavers with the inner near the endodermis (f). In older 

 roots six or seven of the cells in the outer part of the phloem acquire ' 

 thickened walls though the thickening is never considerable. They 

 seem to approximate to a schlerenchymatous nature, but scarcely 

 typical stereome. Though there is now much difference between the 

 outer layer of the stem and that of the young root, that of the latter 

 with age is strikingly angled and the layer immediately under the 

 epidermis has the appearance of palisaded cells, both layers being 

 devoid of chlorophyll. That this layer may have arisen by subse- 

 quent periclinal division is not improbable but was not definitely 

 determined (Fig. 2). 



The pith of the root is devoid of intercellular spaces as found 

 in the cortex. 



RHIZOME. 



While there does not seem to be any considerable difference 

 in structure between the emersed and the submersed part of the 

 stem, there is considerable variation between these and that 

 part of the plant axis which creeps and roots under the mud and 

 may be designated as the rhizome. This is never proportionately 

 as thick and to the naked eye or under a common lens has an in- 

 ternally different structure, being devoid of the central inter- 

 cellular space, while the cortical spaces are fewer and smaller. 

 (Fig. 6 and 7). The librovascular bundles are of the collateral 

 open type and the xylem is strictly pentrach and endarch (Fig. 

 5 and 6). The cambium forms a rather perfect circle in cross 

 section, developing interiorly somewhat bricklike cells in the 

 interfascicular part (medullary rays), the cells inwards passing 

 gradually into those of the pith. These cells are much in appear- 

 ance like the cells of the bundle and are thickwalled. The ducts 

 in each bundle are in several series instead of only one as in the 

 rest of the stem. On the outer part of the phloem there are a 

 few layers of schlerenchyma fibres and just outside in the cortex 

 an occasional latex tube. The interfascicular cambium dips 

 inwards but little. 



THE STEM PROPER. 



The differences between the stem proper and the creeping 

 rhizome have been noted alreadv. The intrastelar fundamental 



