612 BOWMAN— ECOLOGY AND 



titious roots is, of course, the injury or removal of the tip of the 

 root. 



Root hairs are lacking in Rhizophora, as in most all aquatic 

 plants, but their function is fulfilled by many tiny roots which grow 

 out from the subterranean or submarine absorptive roots. These 

 absorptive roots are quite different from the aerial part of the prop- 

 roots or those dependent from the branches (see Fig. 4 and 6, PI. 

 VIII.) These roots are mostly rather short and thick, fleshy, and 

 whitish or pinkish in color, and of a soft texture. 



The extra thickness of these subterranean absorptive roots is 

 due to the greater development of the primary cortex. In the 

 absorptive root this is of large loose cells with very large open inter- 

 cellular spaces in which idioblasts or trichoblasts are lacking. Ex- 

 ternally as Solereder*^'-^ has shown, the periderm consists in this 

 absorptive root only of cork cells, while the same tissue in the 

 aerial portion has both cork and " parenchymatic separation tissue " 

 alternating. 



The cortex of large round cells has been studied by both Van 

 Tieghem and Solereder, and even figured, but it is supposed that the 

 material was not fresh and the delicate cells of the cortex were 

 shrunken (PI. lA^, Fig. 3). These cells are closely connected with 

 the absorption of water, presumably growing as the plants do in salt 

 water of a rather high concentration, shrunk on being placed in 

 reagents of dift'erent densities. At least in the preparation of 

 material for this paper such has been the case and only in material 

 freshly sectioned and mounted in glycerine water could the true 

 idea of the structure of this cortex be gained. The cells compose 

 a loose network and have very large open spaces between them. 

 Some cells are converted contiguously in strands, others radiate 

 about short groups of cells, which are much elongated in the 

 direction of the axis of the root (PI. I., Fig. 4). These elongated 

 cells are often quite full of starch grains, while the large roundish 

 turgid cells radiating from them contain relatively few starch 

 grains and more nmcilaginous protoplasm which stains slightly 

 with water eosin. These round cells, when slightly shrunken due 



*''• Solereder, H., '" S3-stematische Anatomie dcr Dicotj'ledonen," p. 384, 



