EOT— Vol. I.] CAMPBELL— NAIAS AND ZANNICFIELLIA. 51 



probably always undergo regular quadrant divisions, and then 

 each quadrant cell divides into an inner and an outer cell, the 

 former contributing to the plerome. The separation of the 

 dermatogen follows next, and this is soon followed by a 

 second periclinal wall within the periblem, which thus 

 becomes two-layered. All these tissues are more clearly 

 defined in the root region of the embryo than in either the 

 cotyledon or stem (fig. 118). The plerome extends only to 

 the limits of the third primary segment, as in Naias, and 

 from the fourth segment is developed the layer of periblem 

 cells, and later the dermatogen. From the two segments 

 below this layer are formed the cells of the root-cap, which 

 is a conspicuous feature of the root. In most of the sections 

 of the older embryos examined, there was a single layer of 

 initial cells, common to dermatogen and periblem (figs. 122, 

 123), so that directly at the apex the plerome was separated 

 from the inner cells of the root-cap only by a single layer 

 of cells; but finally there is developed a dermatogen con- 

 tinuous over the apex and distinct from the periblem initials, 

 such as we have seen occurs in the roots of the adult plant. 



The end of the root is broad and truncated and the root- 

 cap forms a lenticular body covering only the middle of the 

 flattened root-apex (figs. 122, 123). At the time that 

 the embryo is fully grown, the root-cap is about four cells 

 thick in the middle where the growing part is situated. 



The plerome is very sharply defined in the root of the 

 fully grown embryo (fig. 123) and is more massive than in 

 Naias. It does not show any evidence of a single initial 

 cell at the apex, nor was any sign of the formation of 

 tracheary tissue observed in any of the embryos examined. 

 This probably is first formed after germination begins. 



X. The Endosperm. 



The endosperm formation corresponds very closely to that 

 described for Naias. There is probably a fusion of the 

 polar nuclei, but this could not be positively shown in all 

 cases, and possibly may not always take place. As in 



