334 Evolution in the Plant Kingdom. 
final result is, that in the flowering plant we are considering, highly 
specialized sets of organs produce the two kinds of asexual spores, 
which have been called pollen-grains and embryo-sacs, It seems 
strange to be forced to give up pollen-grains or embryo-sacs as 
sexual affairs, for in our old notion of things they represented thre 
very essence of sex; but the fact remains that they are asexual 
spores and simply give rise to prothallia which bear the sex-organs 
and give rise to the sex-spore. i 
The two prothallia which are developed from these asexual spores 
- have reached the highest degree of reduction, developing within 
the spores themselves. In the case of the pollen-spore two or more 
cells. are developed, which may be easily seen by the use of the 
proper reagents, and this small group represents the male prothal- 
lium, one of the sex-phases in the life cycle. This much reduced 
plant sets apart one or more of its cells to do vegetative or growth 
. work, and another to be the male organ. A very vigorous growth 
of this prothallium is demanded in the development of the pollen- 
tube, through which the male cell discharges its contents. This 
pollen-tube does not usually find an open passage-way, but one that 
is blocked up with spongy tissue, called “conductive tissue,” 
through which it makes way like a parasite invading the tissues of 
a host plant. 
In the case of the embryo-sac, the female asexual spore, the 
development of the prothalliumr is still feebler, the cells representing 
it not only being few in number, but free from each other,—a sort 
of disorganized tissue. The cells representing the female organs 
are clustered near the apex of the embryo-sac, forming what we 
now call the “ egg-apparatus,” while those that probably represent 
the vegetative cells of the prothallium -are clustered at the other 
end of the embryo-sac, and are styled “ antipodal cells.” In pines, 
representing the lowest group of flowering plants, the female pro- 
thallium is a very distinct and compact tissue, bearing regulation 
female organs, the so-called “corpuscula.” This but shows their 
position upon the lower border line of Phanerogams. The sex- 
phase in the life cycle, therefore, which in mosses stood for the 
whole plant as we ordinarily recognize it, in Phanerogams has 
become reduced to little clusters of cells developed within the 
pollen-spore and embryo-sac, so inconspicuous that it has remained 
for the modern reagents to discover their existence. The real sex- 
