SWEET-CLOVER SEED. 
2, and 3.) In general, the development of the embryo sac proceeds 
in the ordinary way, as described by Young (44, p. 133), with the 
inner megaspore functioning. (Text fig. 4 and PL II, fig. 1.) In its 
development the nucellus is destroyed rapidly, the destruction being 
most rapid first at the micropylar end proceeding backward. The 
nucellus is completely destroyed at the micropylar end by the time 
the embryo sac is mature, and consequently the embryo sac comes in 
contact with the outer integument in this region. (PL II, fig. 1.) 
As the destruction of the nucellus extends toward the chalazal end 
the embryo sac becomes much elongated and tubelike. The antip- 
odals disappear early, so that a mature embryo sac consists of the 
egg, the synergids, and the two polars. The two polars lie in contact 
in the micropylar end of 
the sac near the egg until 
fertilization. 
STERILITY OF THE OVULES. 
In Melilotus alba and M. 
officinalis there is very 
little tendency toward 
sterility of ovules. In an 
extended study of ovules 
developing under normal 
and under excessive mois- 
ture conditions only an 
occasional one was found 
in which no reproductive 
cells were differentiated, 
and no ovaries were found 
in which all of the ovules 
were sterile. 
Fig. 4. — Median section through an ovule, showing the embryo 
sac with four nuclei and the position of the integuments. 
X150. 
DEVELOPMENT OF THE POLLEN. 
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9f[d 
The pollen mother cells do not separate, but previous to the reduc- 
tion division the protoplasm shrinks from the walls, thus forming a 
dense globular mass which often occupies less than half the lumen of 
the mother cell. (PL I, fig. 4.) Nuclear division occurs while they 
are in this contracted condition, and four nuclei are formed from two 
successive divisions. The cytoplasm is equally distributed around 
each nucleus. The four masses of protoplasm separate, and as they 
enlarge a number of times and develop into mature pollen grains they 
become binucleate, and a wall is gradually formed around each. 
(PL I, figs. 5 and 6.) At first the cytoplasm is quite dense and con- 
tains some starch but no fatty oils. However, the cytoplasm of 
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