APRIL 5, 1901.] 
embryo-sac when ready for fertilization he 
recognized two groups of nuclei lying re- 
spectively at the poles, which we now regard 
as the egg apparatus and the antipodals. 
At the micropylar end of the embryo-sac 
Hofmeister found usually two nuclei which 
he called ‘germinal vesicles,’ or ‘embryo- 
nal vesicles,’ one of which developed the 
embryo after the entrance of the pollen 
tube. In the opposite end he found a va- 
riable number of antipodal-cells. The em- 
bryo-sac was by him considered homolo- 
gous with the macrospore of the higher 
Pteridophytes. The germinal vesicles cor- 
responded to the corpuscula (archegonia) 
and the accompanying rosette of cells 
(neck) in the gymnosperms. 
Schacht (Jahrb. f. wiss. Bot., 1857-8) 
believed that one of the germinal vesicles 
received the pollen tube and conveyed it 
later to the other, or that in some cases a 
third was present when two germinal ves- 
icles seemed to convey the pollen tube to 
it. The germinal vesicles were sometimes 
marked on their surface by parallel folds, 
or in other cases there were parallel striz 
in their contents. These striz or folds 
formed his ‘ filiform apparatus,’ which came 
later to be recognized by Strasburger, Prings- 
heim and others as homologous with the 
ventral canal cell of the pteridophytes. 
This gave rise to a further conception of 
the embryo-sac which was held by some 
down to a late period, and even appeared in 
some of the earlier editions of Sach’s Lehr- 
buch der Botanik. In addition to the em- 
bryo-sac being a macrospore, it represented 
a prothallium in which the germinal vesicles 
formed the archegonia, while the antipodals 
formed the sterile remnant of the prothal- 
lium which was homologous with the endo- 
sperm of the gymnosperms. 
In 1877-78 there appeared three works, 
by Strasburger, Warming and Vesque, 
which mark another important epoch in 
our knowledge of the embryo-sac. These 
SCIENCE. 
531 
were concerned with the development of 
the embryo-sac, and led to new and quite 
divergent views that have been presented 
from time to time since that period. 
Strasburger (Ueber Befruchtung und Zell- 
theilung, 1877) gave the more complete ac- 
count of the development of the embryo- 
sac and the origin of the endosperm, while 
Warming (De L’Ovule, Ann. d. Sci. Nat. 
Bot., 6 ser.,5) and Vesque (Développement 
du sac embryonnaire des phanerogames 
angiospermes, Ibid., 6 series, bot. 6, 1878) 
were more concerned with determining the 
origin of the embryo-sac in relation to its 
homologies with the pollen mother cells. 
_It is not my intention to outline the history 
of the studies of the embryo-sac further, 
since it becomes very complex and would 
be filled with tedious detail. It is my pur- 
pose, however, to call attention to the prin- 
cipal theories that have been put forward 
in the interpretation of the homologies of 
the embryo-sac. 
It should be borne in mind that in re- 
viewing some of these theories of the em- 
bryo-sac which have been proposed from 
time to time, it is done in no spirit of criti- 
cism, nor for the purpose of ‘holding up to 
view, at the present time, interpretations of 
morphological structures which the authors 
themselves may not now hold. Undoubt- 
edly they were proposed by the authors as 
working hypotheses upon which to build 
further investigations, and it is certain that 
they all have been very useful in stimulating 
renewed and more profound researches, with 
improved methods of technique, and out of 
it all shall come in the future a clearer in- 
sight into the true meaning of these obscure 
plant structures. It is the history of all 
progressive science, that theories are pro- 
posed as working hypotheses, upon which 
to build further investigations into the 
nature of truth. When these have fallen 
new ones are formulated, for without some 
formulated idea in the mind, as a working 
