ApRIL 5, 1901.] 
of development. How then does the em- 
bryo-sac of angiosperms arise? It arises 
directly from the nucellar (sporangial) 
tissues or from the archesporium, without 
the intervention of spores. In the pterido- 
phytes such phenomena are classed under 
the head of apospory. The origin of the em- 
bryo-sac directly from sporangial tissue, 
considered only from the standpoint of the 
absence of spores, would also fall under the 
general category of apospory. But apos- 
pory merely does not indicate the real 
morphological significance of its derivation. 
It is to be interpreted as an adaptation of 
the plant in developmental processes under 
the influence of the changed and peculiar 
environment of the gametophyte, which has 
become so general in the angiosperms, and 
probably in the gymnosperms also. 
There is no longer any need of spores, as 
such, in the development of the female 
prothallium of angiosperms. Where spores 
exist, as such, they exist for the purpose of 
distribution of the plants, as in the bryo- 
phytes and pteridophytes; in the sperma- 
phytes for the distribution of the male 
prothallia, so that they may be lodged in a 
position where the sperm cells may reach 
the egg. There is a law in the evolution of 
organisms and organs, that when an organ 
or structure is no longer needed as such, 
it tends to disappear. Spores are not 
needed in the development of the embryo- 
sac. They are therefore cut out of the 
cycle of development, and the embryo-sac, 
or gametophyte arises directly from the 
tissue of the sporophyte. 
In suggesting that the origin of the 
embryo-sac is a kind of apospory, we do not 
mean that it is phylogenetically connected 
with cases of apospory in earlier forms, nor 
that it is derived from them, nor that apos- 
pory as a phenomenon is continuous through 
groups. Wesimply mean that there has been 
a shortening in the process of development 
here, before the formation of the spores, 
SCIENCE. 537 
just as there has been a shortening after 
the beginning of the gametophyte, and it 
has gone so far that the spore, as such, 1%. ¢., 
a spore which is formed by the accompani- 
ment of the same phenomena which we 
know to prevail universally where we can 
recognize a definite spore, is wanting. 
There is no need that such a spore or 
cell should be formed, because the necessity 
for it has disappeared. A cell, however, is 
formed which is not the morphological 
equivalent of a spore, but is the physiolog- 
ical equivalent, and develops the embryo- 
sac. The process is shortened so that the 
spore is cut out, and perhaps the mother 
cell forms the embryo-sac directly, a new 
development of a prothallium, or body 
functioning as such, directly from sporog- 
enous tissue. : 
If Vines’ suggestion (Student’s Text- 
Book of Botany) that in Asclepias each cell 
of the pollinium is a mother cell, is correct, 
we should have a similar shortening pro- 
cess in the development of the male gameto- 
phyte. But this suggestion may not, 
possibly, be supported by the facts when 
we know the course of development of the 
pollinium and sperm cells in Aseclepias. But 
we can conceive of a hypothetical case 
where a mechanism might arise for trans- 
porting the archesporium from an anther 
to the pistil bodily, and that the reduction 
in the anther had consequently gone so far 
that the tetrad divisions of the mother cell 
to form spores had ceased, now that there 
ig no need for the individual and separate 
spore. The cell of thearchesporium might 
form the pollen tube or male prothallium 
directly, cutting out the spore. This would 
be apospory so far as the loss of the spore 
is concerned. Its significance, however, 
would be greater. It would represent a 
new attainment in the evolution of the 
male gametophyte, quite independent of 
any phylogenetic relation to processes of 
development in earlier gametophytes. 
