SUMMARY. 85 
be distinguished on the outer surface of the band which ultimately 
grow into cilia. 
(18) While the growth ana division of the central cell has been 
taking place tissue changes have occurred in the upper part of the 
nucellus and the pollen-grain ends of the pollen tubes have grown 
down so that they hang free into the archegonial chamber over the 
neck cells of the archegonia. In fecundation the pollen tubes grow 
down until they crowd against the neck cells, and, being under severe 
tension, burst and discharge the spermatozoids over the archegonia. 
The fluid for the swimming of the spermatozoids is surely formed in 
part from the pollen tube and may be partially formed by extrusion 
from the egg cell. 
(19) The mature spermatozoids are the largest known to occur in any 
plant or animal, being visible to the unaided eye. Their motions have 
been carefully studied by keeping them alive in sugar solutions. They 
are ovate or nearly spherical, the apex of the ciliferous spiral being 
usually more or less pointed. Their motion is mainly by the aid of 
the cilia, but besides this they have a sort of selective amceboid 
motion of the spiral end. 
(20) In fecundation the entire spermatozoid enters the egg cell, 
swimming in between the ruptured neck cells. Sometimes two or 
three spermatozoids enter the same egg, but only one is used in 
fecundation, the others perishing. 
(21) On entering the upper part of the egg cytoplasm the nucleus 
escapes from the spermatozoid, being left slightly in rear of the active 
ciliferous band. The plasma membrane of the spermatozoid entirely 
disappears, seeming to unite with the cytoplasm of the egg, and this 
allows the spermatozoid cytoplasm also to unite with the egg cyto- 
plasm and leaves the nucleus free. The ciliferous band remains at the 
apex of the egg cell in the cytoplasm and the nucleus passes on to the 
egg nucleus, with which it unites. 
(22) Fecundation thus consists of a fusion of two entire cells—cyto- 
plasm with cytoplasm and nucleus with nucleus. 
(23) The first division of the egg nucleus has not been observed, but 
the second and later divisions have been carefully studied. In no case 
of the cleavage divisions has any centrosome been observed or other 
body at the pole of the spindle which might be confused with a cen- 
trosome. The development has been followed until the embryo is 
fairly well organized, so that it may be concluded that there is no cen- 
trosome present in the divisions closely following the first cleavage of 
the egg nucleus. It is certain that the ciliferous band, which repre- 
sents the blepharoplast of the spermatid, has no function in the forma- 
tion of the first cleavage spindle or the spindles in any of the divisions 
immediately following, as it remains intact at the apex of the egg 
cell until the egg nucleus has divided into very many small nuclei. 
