1900] LIFE HISTORY OF SILPHIUM II5 
These recent investigations prove that the occurrence of 
spermatozoid-like male cells in Angiosperms is not so rare as 
was once supposed. 
The pollen tube passes along the outside of the cap which 
usually crowns the embryo sac (fig. 64), and enters the sac just 
beyond its free margin. One of the synergids now begins to 
disorganize, and soons becomes unrecognizable. The other 
usually persists for a considerable period, lying against, or partly 
covering, the suspensor of the young embryo. When seen in 
side view this might easily be taken for a pollen tube, as in 
fig. 66, for example. But a little familiarity with the type soon 
removes this source of error, as the pollen tube is much more 
slender. Where the synergid can be seen passing up within the 
cap, as in fig. 67, there is no chance for uncertainty as to its 
identity. That neither of the synergids may be disorganized 
until fertilization is accomplished is shown by fig. 65. 
The recent accounts of fertilization in Lilium, already cited, 
suggested that a careful study of the behavior of the spiral male 
cells of Silphium would be very desirable. Unfortunately, the 
most favorable preparations showing male pronuclei in the 
oosphere were in S. daciniatum and S. trifoliatum, the two species 
in which the elongated cells were not found. Preparations of 
the other species, showing the nuclei in the tip of the pollen 
tube, indicate that the sex nuclei have resumed a spherical form. 
By the growth of the male pronucleus it acquires a close resem- 
blance to the egg nucleus before fusion occurs. 
DEVELOPMENT OF THE EMBRYO. 
After fertilization the oospore develops a wall, and elongates 
rapidly. Its proximal end is occupied by a large vacuole, while 
its distal end is filled with a mass of protoplasm containing the 
nucleus. 
The first wall in the oospore is transverse, as usual, and 
Separates a large proximal vesicular cell from a smaller terminal 
cell. It will be of interest to note that the primary endosperm 
Nucleus divides before the first wall appears in the oospore 
