Oogenesis & Embryogeny in Ephedra distachya. i 71 
cells at a very early stage ; and the functional embryo is described 
and figured as lying at the base of a columella formed from the cells 
of the central region of the embryo-sac. A simple explanation of 
this situation of the embryos, which are said to arise directly from 
the pro-embryos, outside the archegonium is, that they have 
themselves been developed from jacket cells constituting part of the 
central column of tissue around which the arehegonia are grouped, 
for it is just these cells which are often most active in forming 
abnormal pro-embryos in E. distachya. 
If the jacket cells do assume the function of embryo-formation 
both in Ephedra distachya and' E. helvetica, as appears to be 
the case, and this mode of embryogeny is not a mere occasional 
abnormality, we have within the limits of the genus an interesting 
transition series from a truly Gymnospermous organization of the 
ovule as described by Strasburger for E. altissima to a form which 
leads directly on to that of Welwitschia. A mere reduction in size 
of the egg-cells, and a failure of the primary neck-cells to divide 
more than once or twice, both of which conditions are occasionally 
found in Ephedra distachya, would result in the presence of a mass 
of tissue in the apex of the prothallium, nearly all the cells of which 
would be capable of fertilization by the pollen-tube. Such a 
condition is present in Welwitschia, for Professor H. H. W. Pearson 
in his recent paper regards all the cells of the fertile apical region as 
“ potentially equal, though some do not produce prothallial tubes.” 
These fertile cells in Welwitschia also show a marked resemblance 
to the jacket cells of Ephedra, in their multi-nucleate condition, 
which is believed to arise by the amitotic division of the original 
single nucleus. Should Professor Pearson’s further investigations 
prove that a pro-embryonal cell is formed within the tubular cells 
after fertilization there will be little doubt that such cases as this 
among the species of Ephedra are real links between the typical 
Gymnosperms and this genus. 
Also, though this much specialized, isolated group of plants is 
not, in all probability, in the direct line of descent of angiospermous 
plants, yet the embryogeny of this species of Ephedra does suggest 
a process of evolution by which the archegoniatae may have given 
rise to forms in which the archegonium, as such, does not appear. 
Summary. 
In Ephedra distachya the megaspores appear to be arranged in 
a tetrahedral, and not in a linear manner as in E. trifurca. 
The integument arises first on the posterior side of the ovule, 
and only later anteriorly. 
