Oogenesis & Embryogeny in Ephedra distachya. 129 
six-nucleate embryo-sac, shows at a later stage a similar inequality 
of development of the integument. 
Numerous slides showed older embryo-sacs with free nuclei 
lying in the parietal protoplasm ; in one, spindles are present, and 
all the sixteen nuclei show the same phase indicating that in the 
early stages at least there occurs that simultaneous division of 
the nuclei so emphasized by Jaccard in his account of E. lielvetica 
(2). This stage in the development probably extends over a con¬ 
siderable period of time, as it is not until the embryo-sac 
contains about a thousand nuclei that wall-formation commences 
by the growth inward of tubular alveoli. A pyramidal group 
of these at the top of the embryo-sac is soon enclosed by 
the growth of the neighbouring tubular cells ; these are somewhat 
richer in protoplasm than those adjoining them, and their nuclei 
soon return to the outer end of the cell abutting on the periphery 
of the embryo-sac (Fig. 3). This points to an early differentiation 
of the region which gives rise to the archegonia and jacket cells, 
which constitute, in the mature embryo-sac, a well-defined conical 
mass of tissue bounded by rows of cells, each row being evidently 
derived from a single tubular cell. 
In the part of the embryo-sac below this region the tubes grow 
inward till they meet in the middle, the outer wall of the sac mean¬ 
while becoming slightly thickened. After the first filling of the sac 
with this delicate tubular tissue, cell-formation goes on much 
less freely and rapidly in the upper than in the lower part, which 
encroaches upon the tissue lying below the level of the insertion of 
the integument. Just at that level, however, the prothallium always 
shows a constriction, and at later stages assumes an hour-glass 
shape similar to that of the embryo-sac of Gnetuin gnemon. Here, 
however, the larger upper part is not vacuolate as in that genus, but 
filled for the most part by a tissue consisting of the alveoli 
closed and divided by a few transverse walls. 
Ultimately the prothallium becomes differentiated into the 
regions distinguished by Dr. Land according to physiological function 
as haustorial, storage, and archegonial regions, the two first lying 
mainly below the constriction. Hardly sufficient distinction, 
however, seems to have been drawn by Dr. Land between the upper 
part of the prothallium generally, which can be described as “very 
loosely organized” with cells which “are very vacuolate and in 
consequence have little contents,” and the compact conical mass of 
archegonia and jacket cells near its apex, constituting a compara- 
