STUDIES OF THE DEVELOPMENT OF PEPEROMIA HISPIDULA 377 
chalazal end, which in the ripe seed consists of 3 or 4 layers of cells 
below the embryo, very soon thins out to leave but i or at most 2 
layers to separate the tips of the two cotyledons from their food supply 
in the perisperm (fig. iii). Whether this latter thinning out is due 
entirely to the crushing and absorption of the cells of this part of the 
endosperm by the embryo, or may be due in part also to the displace- 
ment of these cells was not determined with certainty. It seems to be 
due chiefly to the former process. This thin layer of tissue,'^between 
the absorbing tips of the cotyledons of the embryo and its food supply- 
in the perisperm, has an evident advantage in allowing the more ready 
transfer of this material to the embryo. 
The character of the contents of the chalazal endosperm cells 
remains similar to that of the endosperm cells of the mature seed. 
The protoplasm is dense with small vacuoles and the nuclei are large, 
characteristically irregular in shape, and may have 8 or 10 nucleoli 
each. It seems clear from their persistence in this position, and from 
the characters just mentioned that these cells must serve to pass on 
nutritive material from the perisperm and it is highly probable that 
they serve the further function of actively absorbing and digesting the 
contents of the perisperm cells. In other words the scantily developed 
endosperm, though containing little stored food itself, continues to serve 
as nurse for the embryo till the supply of food in the perisperm has 
been handed over to the young sporophyte and the rooted seedling 
becomes self-dependent (see Johnson, 1902, p. 334). The middle 
portion of the barrel-shaped portion of the endosperm remains thickest 
and serves as a plug to stop tightly the opening in the disrupted end of 
the fruit, and so probably completely prevents the entrance of water or 
fungi from without and likewise the escape of any dissolved food 
material present between the endosperm and perisperm. The cells of 
the upper exposed half of the endosperm mass, especially the outer 
ones, are much larger than those below. They also have much larger 
vacuoles and where exposed have thick outer walls. These characters 
all seem to make this part of the endosperm jacket a more adequate 
protection against desiccation or other injury to the delicate embryo 
within (fig. III). 
When the endosperm has reached a length of 600 or 700 ^ it ceases 
to "grow, and as the embryo continues its elongation the radicle is 
forced through the opening in the endosperm at the micropylar end, 
pushing aside such remains of the parietal tissue and style as may have 
been clinging to this end of the endosperm jacket. 
