10 IOWA STUDIES IN NATURAL HISTORY 
highly suggestive of the condition frequently observed in Utric- 
ularia vulgaris. 
FERTILIZATION 
Fertilization and secondary fertilization were noted in many 
ovules. The union of the sperm with the fusing polars is 
promptly achieved and the primary endosperm nucleus has 
usually passed to the telophase of its first division before the 
fusion of egg and sperm is completed. The whole series of 
events moreover moves rapidly. The upper ovules, nearer the 
place of exit of the pollen tubes from the stylar canal, have 
developed their first cells of endosperm before eggs in lower 
ovules have been fertilized. There is thus presented a wide 
range of stages in each ovary, though the distance from the top 
to base of placenta at this age is less than two millimeters. In 
other words, fertilization, double fertilization, and the first di- 
vision of the primary endosperm nucleus may take place while 
the pollen tubes travel a distance of two millimeters. It might 
be, of course, that the earlier tubes are all taken by the upper 
ovules, but the method of pollination and the mass of pollen 
tubes implies excess numbers of tubes. 
The cyst containing the fusing egg and sperm is generally 
more or less completely enwrapped by the gorged synergids, 
which are opaque with any protoplasmic stain (Figs. 8, 9). The 
second sperm uniting with the fused polars lies near the egg- 
eyst (Fig. 8), within the protoplasm of the embryo-sae. 
THE ENDOSPERM 
The primary endosperm nucleus divides soon after triple 
fusion and before egg and sperm have completely united (Fig. 
9). Following this first division, a diaphragm is laid down 
across the embryo-sac separating the two daughter nuclei. The 
endosperm now displays great aggressiveness and with further 
divisions soon pushes its way out of both ends of the embryo- 
sac. 
The innermost of the initial pair of endorperm nuclei di- 
vides repeatedly, with cleavage of the protoplast and develop- 
ment of cell walls (Fig. 12). The endosperm presses sharply 
