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1910] SAXTON—WIDDRINGTONIA 39 
After they are formed, the pollen tube renews its activity and rapidly 
grows until it reaches the megaspore membrane. It is only rarely 
that the apex of the membrane is penetrated; more commonly the 
tube grows down a little farther before entering the prothallus. The 
entry is however almost invariably effected before the commencement 
of wall formation, the latter usually taking place only after the tube 
has taken up its final position. At the point where the pollen tube 
pierces the megaspore membrane, a slight constriction almost invaria- 
bly occurs, while the tip of the tube dilates a little to form a kind of 
vesicle just within the prothallus. Preparations are often met with 
in which the contents of the tube are just opposite the constriction, 
indicating a certain amount of difficulty in passing this point. Inside 
the prothallus the wall of the tube becomes thicker (fig. 33). When 
the difficulty of passing this point is overcome, the tip of the tube 
rapidly advances to about, or a little beyond, the middle of the pro- 
thallus. During the whole later growth of the tube the individuality 
of the body cell is less evident than at the stage shown in fig. 32, and 
its cytoplasm may be quite indistinguishable from the rest of the tube 
cytoplasm. A case of this kind, in which all three nuclei are imbedded 
in a common mass of cytoplasm, has already been figured (10, fig. 10), 
and is not uncommonly met with (see also fig. 33). 
Perhaps the most usual case is shown in figs. 34 and 35. Here the 
body cell is distinct, not only from the surrounding cytoplasm: of the 
tube, but also from the cytoplasm in which the sterile nuclei are 
imbedded. With the triple stain, the cytoplasm of the body cell 
stains red, that in which the sterile nuclei are situated takes the orange, 
while the rest of the tube cytoplasm is a deep violet. In later stages 
the body cell increases very considerably in size. Its structure shortly 
before division has already been described and figured. Some 
uncertainty was expressed as to the fate of the two sterile nuclei. It 
was suggested that they were probably absorbed by and became indis- 
tinguishable from the cytoplasm. Later preparations have in the 
main supported this view, but sometimes these nuclei are recogniz- 
able in connection with a quite mature body cell, in a prothallus in 
which wall formation is complete. 
Only a single preparation has been obtained showing the two male 
cells fully organized (figs. 36 and 37). Each cell is surrounded by 
