PHYSIOLOGY OF THE RED MANGROVE. 613 



to a partial plasmolysis, show, on focusing at different levels, the 

 lower wall and its line of juncture with a cell beneath or on the 

 side, this artifact produces a double line of tension or wrinkle on 

 the wall which seems like a tube or channel contained within the 

 cell. Warming regarded these as thickenings for support within the 

 cells which prop the cells apart and assist the soft tissue of the 

 root in maintaining its shape and as they do not appear along the 

 wall separating an intercellular space this artefact seems to really con- 

 firm this view. But since these " verdickungsleisten " are not seen 

 in freshly sectioned and water mounted material, Warming's theory 

 of lateral mechanical support for these cells is not tenable. Mate- 

 rial carried up in balsam or glycerine jelly does show this peculiar 

 irregularly " branched thickening," but it can only be regarded as 

 an artefact. The tissue of this cortex seems to function as a trans- 

 fusion tissue. Warming and Solereder also both state that the tri- 

 choblasts are lacking in the absorptive and tertiary roots, but on 

 close examination some may be found scattered in the xylem ele- 

 ments of the vascular bundle. 



In the aerating prop-roots and those dependent from the 

 branches which have not yet reached the water the cortical area is 

 filled with trichoblasts and large tannin-containing cells "(see Figs. 

 I and 2, PL I\'.). These trichoblasts are frequently branched and 

 double or H-shaped, the branches running up in the intercellular 

 spaces. The tannin cells are larger than the cortical parenchyma 

 cells and on longitudinal section appear as long chains of dense, 

 dark, solidly filled cells. 



The endodermis is easily recognized in either transverse or lon- 

 gitudinal sections by its loose clear structure, the walls being thin 

 and rather more regular than the cells of the cortex, and show the 

 slight irregularities in the wall that Warming mentions and calls 

 " the Caspar spots." In the older roots the endodermis is crushed 

 by the secondary growth so as not to be recognizable. 



The central vascular cylinder of these aerating roots shows sev- 

 eral interesting peculiarities. If sections are made from regions 

 just behind the root cap and then a region several centimeters back 

 and finally of an older root, striking differences are noted. In the 

 figure given (Fig. i, PI. IV.), the section has been cut about three 



