7 
92 COMPARATIVE EMBRYOLOGY OF THE RUBIACEAE 
of haustorial cells by the embryo in Callipeltis is not so great as 
in Vaillantia, either in point of number or size. With the de- 
velopment of the embryo proper and of the endosperm, the basal 
cell elongates, allowing the embryo to take a more central posi- 
tion in the endosperm. The haustorial portion is then near to the 
embryo. The basal cell is finally crushed between the cells of 
the endosperm, the haustorial portion becomes absorbed, so that 
only a single cell is left as a portion of the root cap of the 
embryo. 
The development of the embryo is briefly as follows: After 
transverse division has ceased, the terminal-cell divides longitudi- 
nally once, then a second time. The second cell from the end fol- 
lows suit, then the third and finally the fourth. Meanwhile the first 
three tiers of cells are giving rise to dermatogen, then to plerome 
in the fashion described by many authors for numerous dicotyle- 
dons. The fourth tier of cells which apparently never exceed 
four in number, remain so and may be recognized in the definitive 
embryo as a small protuberance at the top of the root cap. 
A great deal of variation takes place, but the plan just set 
forth is followed in general and the ultimate product is the 
same, 
Sherardia arvensis 
This plant, the only species of the genus, is a small upright 
annual having the whorled foliage of the Galieae with small heads of 
several flowers with rose colored tubular corollas. It is distrib- 
uted in Western Asia, Europe and North Africa. The material | 
for study was obtained in cultivation in Germany and in New 
York. 
The history and character of the nucelli, integument and mega- 
spore mother-cells call for no special treatment. No evidence 
has been obtained pointing to differences in the division of the 
megaspore mother-cells, or in the selection of a given megaspore 
to become the embryo-sac. It thus appears that the megaspores 
are of potentially equivalent value. During migration down the 
micropylar canal the three serial divisions of ‘the embryo-sac . 
nuclei take place and finally a definitive embryo-sac is formed 
which differs somewhat from those hitherto described in form and 
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