52 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
THE ENDOSPERM AND EMBRYO 
The endosperm is at first parietal, and arises by free cell for- 
mation. At a somewhat early stage the central cavity becomes 
obliterated by the growth of the endosperm cells toward the center. 
Walls are then secreted and the tissue then presents in the main 
the same appearance as the endosperm in the 6۵/26۵6, The pe- 
ripheral cells, which are more densely filled with cytoplasm than 
the rest, appear to play the roles of digestive and absorptive cells 
before which the integument breaks down as the endosperm grows. 
The integument breaks down with the usual appearances accom- 
panying histolysis, although the cells of the micropyle resist the 
digestive action rather more than the rest of the tissue. The cells 
of the middle part of the endosperm, as the latter reaches a con- 
siderable size, present, on the other hand, a quite different char- 
acter. They are larger and have contents which stain in such a 
way as to suggest that they also are suffering histolysis. A col- 
umn of such cells extends from the embryo two-thirds of the 
longitudinal distance through the endosperm. As the embryo 
grows in length it comes to occupy this space, displacing the cells. 
The embryo is of remarkably slow growth in the earlier stages 
of its development. The early growth takes place in the usual 
way, forming a suspensor of a few cells which are totally devoid 
of such outgrowths as have been described for the Galicae. The 
spherical form of the embryo proper is reached only slowly, and 
meanwhile the endosperm grows so as to reach nearly its final 
size. The later development of the embryo during which the coty- 
ledons are formed is more rapid. 
Diodia teres 
(PLATE 12, FIGURES 13-17; PLATE 13, FIGURES 1-10) 
THE NUCELLUS AND STROPHIOLE 
With a trifling difference in the configuration of the nucelli, due - 
apparently to the somewhat different mechanical relations in the 
ovary of this species, their behavior and that of the basal partition 
is the same as that in Diodia Virginiana (pl. 12, fig. 13). The in- 
sertion of the funicle, however, is not so far removed from the base 
of the ovary on account of the somewhat less rapid development 
