POLLINATION OF FLOWERS 
669 
far apart that fertilization cannot occur. 
To prevent this loss in part the seed was 
evolved. In the cases of the seed plants 
the large spores were retained in the seed- 
cases, or ovules, and became the center 
around which the seed was built up. The 
small spores are similar to pollen grains, 
altho not so called outside of the seed- 
plants. Thus the production of spores of 
two kinds made possible the development 
of the seed-plants which otherwise would 
not have taken place. It is the second most 
important event in the history of plants. 
THE SEED-PLANTS, OR PLANTS ADAPTED TO 
POLLINATION. 
Pollination occurs only in the seed- 
plants or Spermatophytes. To this group 
belong the conifers or evergreen trees and 
the eycads (Gymnosperms), and The flow¬ 
ering plants (Angiosperms). The Gymno¬ 
sperms are so-called because the seeds are 
naked or unprotected by a seed vessel, while 
in the Angiosperms the seeds are enclosed 
in a case or capsule. The cycads and the 
conifers are derived from the ferns and 
are very much older than the flowering 
plants. In the Mesozoic Age a remarkably 
even climate prevailed over the larger part 
of the land surface of the earth and gymno- 
spermous trees were the dominant type of 
vegetation. The vast forests of this age 
composed of conifers, maiden-hair ti'ees, 
cycads and cycad-like plants, and tree ferns 
must have displayed a foliage which in 
beauty of form has never been equaled be¬ 
fore nor since in a terrestrial landscape. 
There are only 450 living species of Gym¬ 
nosperms, the larger part of which produce 
cones. 
To the Angiosperms belong the hardwood 
trees, as the birches, beeches, oaks, maples, 
and elms; all common shrubs; and a great 
company of herbaceous plants, as the 
grasses, sedges, lilies, pinks, buttercups, clo¬ 
vers, heaths, gentians, mints, asters, and 
goldenrods. The seeds are enclosed in a 
case or ovary; and, as the pollen can not 
come directly in contact with the ovules, 
it is received on a glutinous surface called 
the stigma. 
THE ORIGIN OF THE SEED AND OF POLLINA¬ 
TION. 
As has already been pointed out the 
higher fernworts produced two sorts of 
spores, small spores and large spores. (This 
is well shown today in the water ferns, Mar- 
silia.) The small spores were similar to 
pollen grains, and produced male cells or 
sperms alone. The large spores produced 
only eggs, and were often 100,000 times 
larger than the small spores. The small 
spores were exceedingly numerous and 
were very widely and easily distributed by 
the wind. The large spores were fewer in 
number and contained a reserve supply of 
food, which, after the fertilization of the 
egg, nourished the young plant. .The ad¬ 
vantage of heterospory, or the production 
of two different kinds of spores, was that 
it very frequently ensured cross-fertiliza¬ 
tion. But where both kinds of spores were 
set free, and widely scattered, they were 
many times so far apart when they fell to 
* the ground that fertilization could not take 
place. Thus the waste of spores was enor¬ 
mous. 
To prevent this waste the seed was 
evolved. The first step in its development 
was the retention of the large spore in the 
spore case, called in the higher plants the 
ovule (the seed before fertilization). The 
egg was thus protected by the coats both 
of the spore and the spore-case. The fe¬ 
male plant practically disappeared, or 
rather was reduced to a few cells, one of 
which was the egg. After fertilization the 
egg today gwvvs into an embryo or infant 
plant, consisting of one or two minute 
leaves and a stem. Thus time is saved 
when later the seed germinates. The seed 
is called by Scott the nursery of the infant 
plant. But in the first seeds which were 
formed many million years ago there were 
no embryos.or young plants. They were 
evolved at a later period; but a quantity of 
food was stored in the seed then as now, 
and its contents were protected by the 
hardening of the walls of the spore and the 
spore case. Finally the seeds were dis¬ 
persed in various ways. 
The smaller spores wero identical with 
pollen grains, and were brought to the 
ovules by the wind. In the cone trees the 
pollen adheres to a drop of glutinous liq¬ 
uid or mucilage in the opening at the end 
of the ovule; and in the flowering plants 
to a sticky surface called the stigma. The 
reception and retention of the pollen near 
