266 
MORPHOLOGY 
(Peperomia) there are sixteen free nuclei in the embryo sac. These 
nuclei show no polarity, and a large number of the nuclei enter into the 
formation of the large fusion nucleus, which in this case is the result of 
multiple fusion. This same general condition has been found also in 
Juglans (walnuts), 
Ulmus (elms), the 
aroids, etc. ; but 
probably in all 
these cases two or 
four megaspore 
nuclei are in- 
volved. 
Nutritive mech- 
anism. The nu- 
tritive mechanism 
of the embryo sac 
is varied and some- 
times complex. 
In all cases there 
is an enlargement 
of the sac, which 
encroaches in 
every direction 
upon the adjacent 
tissue of the nucel- 
FlG. 594. Mature female gametophyte of lily within the lus wnich is thus 
anatropous ovule, showing the egg apparatus (e, the egg; the Used as a nutritive 
two other cells the synergids) directed towards the micropyle (m), {jsgue In some 
the three antipodals at the other end of the sac, and the two , , 
polar nuclei in contact in the center. After COULTER. C a S 6 S, r 
among the Sym- 
petalae, there is organized about the sac a definite nutritive jacket, 
which obtains food from the surrounding tissue and from which it enters 
the embryo sac. In other cases the antipodal end of the sac extends 
into the tissue beneath (chalaza), sometimes becoming conspicuously 
tubular and prolonged. In still other cases tubular extensions of the 
sac are put out in other directions, especially into the heavy integu- 
ment from the micropylar end. Occasionally all of these methods of 
nutrition are combined, resulting in a complicated and very efficient 
nutritive mechanism. 
m 
