22 Humphrey . — The Development of the 
cell is soon cut off (tap., Fig. 42), and then divides by anti- 
clinals into a series of cells similar to those of the body of the 
nucellus (tap., Fig. 43). The mother-cell of the embryo-sac 
enlarges as the ovule grows, but does not divide further, and 
thus becomes itself the definitive embryo-sac (e. s., Figs. 43, 44). 
The development of the seed from the ovule follows the usual 
course in its general features, but certain details will repay 
examination. The integuments consist of about six and two 
cell-layers, respectively. The inner coat becomes finally 
reduced to a thin remnant (i. i., Fig. 49). The cells of the 
external layer of the outer one become elongated parallel to 
the surface of the ovule, while those of the internal layer 
lengthen radially (ext., ini., Fig. 47), and become the chief 
protective layer in the ripe testa. When fully developed they 
are empty and have somewhat thickened inner and radial 
walls, while their outer walls remain thin. Peculiar modifica- 
tions of the lateral walls give to this row of cells a very 
characteristic appearance, best understood from Fig. 49 a. 
The cells included between the outer and inner layers con- 
stitute a nutrient layer and become greatly compressed during 
ripening (nut., Fig. 49 a). Just after fertilization, the free end 
of the outer integument and the free portion of the funiculus 
into which it passes at one side of the micropyle begin to swell 
(ar., Fig. 45), and gradually close the micropylar opening, 
compressing, and finally obliterating, the end of the inner 
integument. The mass formed by the coalescence of the 
thickenings grows rapidly, becoming very large and fleshy, 
and finally forms the aril which caps the micropylar end of 
each seed (ar., Figs. 46, 48). From the mode of its formation 
it is evident that it must include the funicular bundle and the 
remnant of the micropyle ; and these may be recognized in all 
stages (m., v. b., Figs. 46, 48). This micropylar aril is of the 
type to which Planchon (’ 45 ) has given the name arillode. 
At an early stage the inner integument has a regular ovoid 
curve (i. i., Fig. 44) ; but about the time of fertilization the 
broadening of the nucellus gives it a prominent shoulder at 
the outer angle (Fig. 45). Just within this shoulder the 
