6 
BULLETIN 844, U. S. DEPARTMENT OF AGRICULTURE. 
just being differentiated and while the outer integuments are barely 
prominent at the base of the nucellus. The pollen grains are formed 
while the embryo sac is beginning to develop. The division of the 
megaspore mother cell does not occur until a number of days later, 
and the embryo sac is not mature until the flower is nearly ready to 
open. Thus, the pollen grains are formed a week to 10 days before 
the embryo sac is ready for fertilization. The pollen grains increase 
in size and undergo internal changes after their formation. These 
changes, which are not completed until the flower is one-half or more 
of its mature length, may be regarded as the ripening processes, and 
they are undoubtedly necessary before the pollen is capable of func- 
tioning. For this reason it is probable that the pollen grains are not 
able to function much before the embryo sac is mature. 
The pistils of Meli- 
lotus alba and M. offic- 
inalis are straight for 
the greater part of 
their length, but curve 
rather abruptly toward 
the keel just below the 
capitate stigma. The 
surface of the stigma 
is papillate. (Fig. 3.) 
In their reaction with 
Fig. 3.-Stigma at the time of pollination, showing its papillate Sudan III, alkanm, and 
character and the position of the pollen in reference to the papillae safranin the Walls of 
in pollination. X 175. ^ ^^ Qf ^ ^ 
ma show that some fatlike substances are present. Aside from water, 
the contents of the papillce consist chiefly of a fine emulsion of oil. 
DEVELOPMENT OF THE OVULES. 
The number of ovules in the ovary of Melilotus alba varies from 
two to five; however, most commonly, three or four ovules occur. 
In Melilotus officinalis the number in each ovary ranges from three 
to six. In both species the ovules are campylotropous at maturity 
with the micropylar end turned toward the base of the ovary. 
Mature ovules contain two integuments, but the inner one does 
not close entirely around the end of the nucellus. The outer integ- 
ument develops considerably ahead of the inner one. The outer 
integument is much thickened at the micropylar end, the seed coat 
is formed from it, and the inner integument is used as nourishment 
by the endosperm and embryo. 
The number of megaspore mother cells in an ovule varies from 
one to many. Two or more embryo sacs often start to develop in 
the same ovule, but seldom more than one matures. (PL I, figs. 1, 
