HOUSTONIA 67 
By growth in all directions the mass of the ovule is increased, 
and finally a bowl-shaped form is attained, with the concave sur- 
face turned toward the placenta. This change in form is accom- 
panied by lengthening of the funicle, which has histologically the 
appearance of being a part of the placenta, but which in reality is 
derived by the regular division of the cells (figs. 8 and ro, ff), 
which constitute a very short stalk in the younger condition, 
It is interesting to note in passing that the “zwcellus nudus” 
of Schleiden, which that botanist incorrectly thought to be found 
in certain Rubiaceae, is realized in Houstonia. 
It must be evident that generalizations made heretofore with 
reference to the occurrence of ovules without integument in de- 
generate plants must fall to the ground. 
THE ARCHESPORIUM 
The archesporium consists of a single large embryo-sac-mother- 
cell, surrounded by a single layer of usually about six small 
slender suppressed ones which show no tendency to divide. They, 
however, do not all degenerate, but some at least take on special 
cytological characters and take up their position in the cavity 
vacated by the functional embryo-sac-mother-cell in its develop- 
ment ( fig. 9). In this figure one may see two such mother-cells 
which have the appearance of glandular cells, resembling in this 
regard the antipodal cells. From the same figure it is also evident 
that some of the mother-cells persist in this character for a con- 
siderable period, until, at least, the completion of the embryo-sac. 
When the growth of the nucellar cap has proceeded until the 
archesporium comes to lie in the middle of the naked nucellus, 
the division of the megaspore mother-cell takes place. Four 
megaspores arise by two divisions, of which, contrary to the 
general rule among the Rubiaceae studied, the basal megaspore 
becomes the embryo-sac cell. In fig. 6, in which the arrow indi- 
cates the egg pole, are shown the four cells, of which the basal 
is the largest. Its sister cell is small, while the remaining pair of 
cells are evidently destined also to be of small dimensions. 
The embryo-sac cell develops into the embryo-sac 7m situ. 
jig. 7 shows the two-celled, and fig. 8 the four-celled, condition. 
The definitive condition is shown in fig. 9. In its growth, the 
