POLLINATION OP FLOWERS 
673 
of the ocean their little shells are silently 
falling- and building up new deposits. 
Fungi, mosses, and ferns produce single 
cells or spores in countless millions, which 
are capable of growing into new plants. If 
conditions admitted, almost any species of 
these groups would speedily occupy the en¬ 
tire land surface. The poplar tree, tulip 
tree, osage orange, raspberry, blackberry, 
and many other shrubs and trees send up 
numerous shoots from the roots. Many 
plants are readily propagated by buds, or 
bulbs, or by the rooting of the leaves or 
stems. Other plants send out numerous 
runners or stolons as white clover and the 
strawberry. So far as numbers are con¬ 
cerned the absence of sex is clearly no dis¬ 
advantage to many plants. 
SEXUAL REPRODUCTION. 
If plants can multiply vegetatively why 
has sex been developed. The first plants 
did not possess sex; it has not taken the 
place of vegetative reproduction. The lat¬ 
ter has always been and is still very ef¬ 
fective. Both methods still exist side by 
side. The offspring of plants which are 
produced without sex are similar to the 
parent form, They vary relatively very 
little, altho there are exceptions. Florists 
and horticulturists take advantage of this 
fact to increase their stock of new flowers 
and fruits by grafts or divisions of the 
original plant, since such varieties grown 
from seed are not likely to be true to name. 
Species which have little power of varia¬ 
tion are clearly at a great disadvantage. If 
conditions change, they can not change with 
them and are likely to perish quickly. They 
can not migrate to new localities since they 
can not adapt themselves readily to new 
conditions. It is difficult to see how the 
evolution of plants could have ever taken 
place without variation, and sex secures 
greater variation. 
The offspring of plants by sexual repro¬ 
duction will inherit the characters of both 
parents, and will therefore be more vari¬ 
able than either. Among the variations 
there are likely to be some which will be 
beneficial, and which will enable the plants 
to adapt themselves to new conditions, and 
to take advantage of new opportunities. 
Variation is necessary for evolution, and 
the greater the variations the more rapid 
the advance. One advantage of sex is, then, 
that it secures greater variation thru cross- 
fertilization. 
Greater vigor in the hybrids also usually 
follows cross-fertilization, as was first 
pointed out clearly by Charles Darwin. He 
was experimenting with two beds of toad¬ 
flax, or butter-and-egg’s (Linaria vulgaris), 
one set being the offspring of self-fertiliza¬ 
tion and the other of cross-fertilization. 
The plants had been raised for the purpose 
of studying heredity, and not the results 
of cross-breeding. To his astonishment 
he observed that the plants which were 
the result of cross-breeding were far more 
vigorous than the others. He temporarily 
abandoned all his other investigations and 
devoted himself to making numerous ex¬ 
periments in breeding, and to acquiring in¬ 
formation as to the practical experience of 
horticulturists and breeders of animals. As 
the result of his inquiries he was convinced 
that no species of animal or plant can fer¬ 
tilize itself thru numberless generations, 
and that an occasional cross is indispen¬ 
sable. 
Hybrids have a greater power of assimi¬ 
lation, a larger root system, and the seed¬ 
lings grow more rapidly and mature ear¬ 
lier. The leaves are larger, the stems are 
stronger, and there are more flowers and 
fruits. Why does the crossing of two 
strains or races produce greater vigor in the 
progeny? The following explanation has 
been suggested by Coulter: In the strug¬ 
gle for existence among plants undesirable 
characters tend to disappear, since the spe¬ 
cies possessing them are eliminated. The 
characters which survive are the most de¬ 
sirable ones. In order to survive a desir¬ 
able character must have vigor, and each 
must add somewhat to the vigor of the 
plant containing it, and in consequence its 
size and productiveness will also increase. 
The plants having the greatest number of 
desirable characters are hybrids, since they 
contain the characters of both parents, 
hence hybrids will show at once a great 
increase in vigor and productiveness. The 
first generation shows the greatest vigor, 
after which, if there is inbreeding, the pro¬ 
ductiveness rapidly falls off. As the re¬ 
sult of inbreeding a race tends to disappear. 
Crossing between flowers on the same plant 
or between plants derived from the same 
