This new cell grows and divides into more cells, thus forming the young embryo of a new plant. This embryo is the living part of the seed and around it usually a great deal of plant food is stored, so that when it begins to grow it will have plenty of nourishment until it is able to develop the roots and leaves necessary to prepare its own food.
Embryos cannot be produced unless pollen grains and egg cells unite, so it is absolutely essential that the right kind of pollen grains be brought to the stigma. Some stigmas are able to use the pollen grains produced by the anthers of their own flowers, but others can only use pollen from other flowers and other plants. It is therefore necessary that these pollen grains be carried about from flower to flower if fertile seeds areMINT FLOWER.
to be produced.
In some cases the pollen is borne about by the wind, as in the case of corn. In this way an exceedingly large number of pollen grains are wasted, as can be seen by the great amount of yellow pollen scattered over the ground of a cornfield when the corn is in bloom. In the corn each one of the corn silks is a pistil and a seed is produced at its base if a pollen grain lights upon the stigma at its upper extremity.
The flowers of walnut and apple trees are fertilized by wind-blown pollen.
The pollen of very many plants, however, is carried about by humming birds, bees and other insects. As the bee crawls into the flower to get the nectar at the bottom, it brushes against the anther and some of the pollen grains become attached to it. These, later,are rubbed off by the rough or sticky stigma of another flower which the bee has entered and thus the flower isfertilized. The humming bird, by reaching its long slenderFig. 98.
beak down into the long narrow tube formed by the corolla of the "wild honeysuckle" (Fig. 98), brushes upon the stigma the pollen grains it has obtained from another flower and thus distributes pollen from flower to flower. In no other way could these plants be fertilized.
The beautiful colors of flowers and the sweet nectars that many of them secrete are the adaptations of the plant for enticing insects to enter them and bring to their stigma the pollen from other flowers, or take from their anthers pollen needed to fertilize another similar plant.
Some flowers are so constructed that only certain insects can fertilize them, the wild honeysuckle requires the humming bird, the red clover the bumble-bee (Fig. 99) and otherplants, other kinds of insects. Flowers of some varieties of plants cannot be fertilized by flowers of a like variety. Certain varieties of strawberries,Fig. 99.
for example, need to have other varieties plantednear them, if they are to prosper. Some plants need not only to have other varieties planted near, but they also require the presence of special insects.
One of the most striking examples of this is the Smyrna fig. For many years attempts were made to introduce this fig into California. The trees grew all right but the fruit did not mature. It was then observed that in the regions where this fig was successfully grown a species of wild fig was abundant and that the natives were accustomed to hang branches of the wild fig in the Smyrna fig trees at the time they were in flower. These wild fig trees were brought to California and grown near the Smyrna fig trees, but still figs did not mature. Upon further examination itwas observed that at the time of flowering
YUCCA OR SPANISH BAYONET.
a small insect issued from the wild figs and visited the flowers of the Smyrna figs. This insect was brought to California and now it is possible to grow figs. The flower of the Smyrna fig has no stamen and it is necessary for the wild fig to furnish the pollen which is only successfully carried to the stigmas of the edible fig by the small fig- fertilizing insect.
A somewhat similar case is that of the yucca found in the dry region of southwestern United States. This flower can only be fertilized by the aid of a small moth which flies about at night from flower to flower. It enters the flower, descends to the bottom, stings one of the ovaries, deposits an egg, then ascends and crowds some pollen on the stigma. The grub, when it hatches from the egg, feeds on the seeds in the ovary, but as there are many seeds in the flower which have been fertilized and the grubs eat only a few of these, the moth has made it possible for the yucca to produce seeds sufficient for its continued propagation, which would be impossible if it were not for the moth.
These are only a few of the vast number of cases which show the close relationship existing between plants and animals and the dependence of the one upon the other.
96.Seed Dispersal. -Not only
must flowers produce fertile seeds, if the plants are to continue to exist, but these seeds must be scattered. To do this the seed pods of some plants suddenly snap open and spread their seeds. Thetouch-me-not and pea are examples of this. In some plants, like the maple, the seeds are winged (Fig. 100) and float for some distance in the air. Others, like the thistle and the dandelion, have light hairlike appendages which enable them to float away. In the case of the tumble- weed (Fig. 101) the plant itself is blownFig. 100.
Fig. 101.
about, scattering the seeds over the fields as it bumps along from placeto place.
Some seeds are provided with hooks or barbs, like the beggar"s ticks (Fig. 100), which attach the seeds to animals so that they are carried to a distance. Seeds having an edible fruit cover, such as the cherry, blackberry and plum, are eaten by birds and animals and the undigested seed deposited far away from the place where the seed grew. Seeds like the acorn are carried about by squirrels and otheranimals. Many seeds are able to float in waterSCRUB OAK BRANCH.
Showing the acorns.
