Oogenesis & Embryogeny in Ephedra distachya. 133 
tube nucleus, the body and stalk cells, and one of the two prothallia- 
cells. It passes down the long neck of the archegonium and usually 
fuses with the apex of the egg-cell, though sometimes it passes 
within it, as shown in Fig. 11. Here the fissure in the tip of the 
tube with the contents passing out is clearly seen, and five small 
nuclei arc lying close by. The functional sperm nucleus has 
apparently already passed to the egg-nucleus, for a considerable 
part of its path may still be traced through the cytoplasm. 
The male gametes were observed, however, in several other 
archegonia ; they are discharged into the egg, lying side by side in 
a common envelope of cytoplasm. The functional one, which is 
at first about 8/x in diameter and twice the size of its companion, 
slips from the cytoplasmic sheath and travels as a naked nucleus 
to the centre Of the egg (Figs 12, 13). On its way it increases 
somewhat in size, becoming more vacuolate, and the chromatin 
collects into irregular masses like those found in the egg-nucleus, 
while the nuclear wall almost disappears. 
The entry into the egg-nucleus was never observed, and the 
condition of the ovules at later stages indicates that fertilization 
was not effected in the majority of cases. A possible explanation 
of this failure is that the entry of the pollen-tube was delayed owing 
to the coldness of the season, and by the time the male gamete 
arrived the nuclear membrane of the female gamete had thickened, 
so that entry was no longer possible. The membrane is very 
definite in these sections, and in several cases, a little bunch of 
fragments of chromatin material, such as might be the remains of 
the male gamete, is to be observed lying just outside it. In 
addition to the two sperm-nuclei about four others appear to be 
discharged into the egg by the pollen-tube, but the latter is so 
obscured by the many neck-cells and the darkly staining products 
of degeneration in its course down to the oosphere, that it has not 
been possible to determine how these arise. 
IV.— Embryogeny. 
In spite of the fact that fusion of the sperm and egg-nucleus 
was never observed, even though many slides showed archegonia 
which had evidently been entered by pollen-tubes, yet nearly all 
the older ovules which were cut contain pro-embryos like those 
described by Strasburger (6). In most cases they seem to be due 
to an apogamous development of the jacket cells, though they 
appear in a few cases to be formed by a normal method of embryo¬ 
geny from the egg, for there is reason to believe that fertilization 
has taken place in some instances ; these latter cases will be first 
described, 
