Box.— Vol. I.] CAMPBELL— NAIAS AiVD ZANNICHELLL4. 29 



possible that the four terminal quadrants may arise as stated 

 by Hanstein and Famintzin, but further investigations are 

 needed to settle this. 



A study of the older embryos of Naias shows that the 

 great bulk of the embryo is derived from the first two seg- 

 ments. The third one, as we have already seen, forms a 

 series of transverse walls; and of the cells thus formed, the 

 two upper ones divide by a series of longitudinal walls, but 

 no secondary transverse walls are formed, at least for some 

 time, so that they form single layers of cells, easily recogniz- 

 able in exact median sections of the older embryos. The 

 lower of the two has only a limited development and forms 

 a small group of cells continuous with the epidermis of the 

 rest of the embryo (fig. 70). The segment above it, like 

 the terminal ones, has first two intersecting median walls, 

 and next, by periclinal walls, the epidermis is separated. 



The differentation of the primary tissue-systems is brought 

 about very early and is especially evident in the middle re- 

 gion of the embryo (figs. 68, 70). The dermatogen, as we 

 have seen, is determined by the first periclinal walls in the 

 upper segments (fig. 65), and this is followed later by the 

 somewhat similar division in the next lower one. The sep- 

 aration of plerome and periblem,is determined in the upper 

 segments by the subsequent divisions, which are longitudinal 

 and divide each of these segments into a group of four cen- 

 tral cells (two when seen in logitudinal section) and a single 

 layer of cells between them and the epidermis — the periblem. 

 The formation of these primary tissues is very regular in the 

 central segment, from which the stem and root are formed, 

 but in the cotyledon they are not quite so clearly defined. 

 Famintzin states that in Alisma there is at first but a single 

 plerome cell in each segment, but Hanstein's figures show 

 an arrangement very similar to that \n Naias, and as Famint- 

 zin studied this from optical sections, it is quite probable 

 that he was mistaken. Even from a study of his own figures, 

 it is difficult to understand how he can have reached this 

 conclusion. In the basal segment of the embryo of Naias 

 there is no formation of a plerome, but all the inner cells 



