290 Ishikawa—Studies on the Embryo Sac 
narrowed tip penetrates the apparatus (PI. VII, Figs. 12, 17); in other 
cases the tube ramifies at the contact surface, reminding one of the pseudo¬ 
podia of Amoebae or clasping fingers, and some of the branchlets proceed 
farther (PL VII, Fig. 18). In such a case it often causes dislocation of the 
filiform apparatus (fit.), which subsequently becomes smothered by the con¬ 
tents of the attacked synergid (syn.) flowing out. The tip of the pollen- 
tube has no special apparatus for pouring out its contents. A small pore 
seems to be in preparation for a time, probably by the action of certain 
enzymes, such as cytase and pectinase, secreted by the male cell, and acting 
upon cellulose and pectic substance, of which the wall of the tube and fili¬ 
form apparatus are composed. Though it is a mere supposition, the same 
enzymes may attack next the filiform apparatus for the passage of the tube, 
and then act upon the wall of the invaded synergid, which thus becomes 
actually perforated, as will be described later on. The contents of the tube 
are poured into one of the synergids (PI. VII, Figs. 10, 12), or often into 
both of them (PI. VII, Figs. 8, 11, 14, 17 ; Text-figs. IV, VII, 3), probably 
owing to the accidental position of the tube end, so that sometimes it causes 
the enzymes to act upon the walls of both synergids. 
The plasm containing starch grains in the pollen-tube is poured into the 
attacked synergid (syn.) as shown in Text-fig. VII, 1-3 ; PL VII, Figs. 8-12, 
37, 18; especially Fig. 17 shows the critical moment of the intrusion 
of those expelled grains. For this reason the grains serve as a clue to trace 
the contents of the tube. Iodine solution is the best reagent for this 
purpose. The intrusion of starch grains from the pollen-tube has already 
been mentioned and illustrated as occurring in Najas major by Hofmeister 
( 28 ) in 1858. He also observed so early as 1847 the migration of starch 
corpuscles from pollen grains to pollen-tubes in several other plants, 
especially in Oenothera , Godetia, and Boisduvalia ( 26 ). 
The invaded synergid becomes much swollen with the additional 
protoplasm, and the contents suddenly get chromatic, but starch grains 
inside are still perceptible. The wall of the synergid bursts, with the 
result that the mixed contents flow out upon the lower part of the oosphere, 
which is thus covered by them for a while. PL VII, Fig. 9 a, represents 
a side view of an attacked synergid (syn.j ; the contents ( p.f.) are just going 
to spread over the oosphere (e.c.) through the several rents (r.) on the lower 
side. Fig. 9 b is another section obtained from the same sac, showing the 
other sound synergid (syn.) and the egg-cell (e.c.), the latter of which is just 
ready for fertilization. Text-fig. IV clearly illustrates an advanced stage : in 
the right-hand one of the twin sacs, the oosphere is totally covered with the 
contents (p-f) of the invaded synergid (syn.), while the disorganized synergid 
nucleus is seen as a spherical chromatic mass (s.n.), and two male nuclei (m.n.) 
embedded in a hyaline plasma sheath (p.s.) are clearly visible, through which 
the egg nucleus (e.n.) is discernible. Figs. 14 and 16, PL VII, represent 
