THE TROPÆOLUM.
Like the morning-glory flower, the tropæolum, or nasturtium, as we usually call it, has several important organs. It has a pistil and stamens, and plenty of rich nectar.
Its corolla, as you know, is large and showy, but it is not in the form of a tube. It is divided, into several distinct pieces called petals. Its calyx, too, is not green, but is colored somewhat like the corolla.
And what is that we see—that long red horn?
That is the tropæolum’s nectary. It is framed from the calyx, in which certain of the sepals have grown together to form this horn of plenty. We are tempted to call it a horn of plenty because it is shaped like a cornucopia and is overflowing with sweet nectar.
It is no wonder the bees and humming birds visit Tropæolum so constantly.
She has provided a most attractive dish of honey for them, but she has so cleverly placed it that they cannot reach it without doing her a service. In our climate bees and humming birds are her constant visitors, but in her own home, in South America, she may have visitors we do not know. She may have a favorite moth whose tongue just fits into her long red horn, or it may be a humming bird that comes to her there, for South America is the home of the humming birds, or it may be a butterfly. We do not know about that, but we do know that her red spur has doubtless grown to its present form to please some beloved bird or insect, and that the bill or tongue of that bird or insect is as long as her red spur.
Why do you suppose Tropæolum makes honey for the insects and the birds?
Why does she love to have them come and take the nectar from her long red horn?
I think I know the reason why. She has placed her horn of nectar just back of her stamens. The bees must walk over the stamens before they can reach the nectar. The humming bird must touch the anthers when he thrusts in his bill. Whatever takes the honey must touch the anthers.
This is why Tropæolum has a long red horn full of rich nectar. She wishes the birds and insects that come to her for honey to touch her anthers, which are overflowing with red pollen.
She has made the pollen for her friends, and not for her own use. She wishes her neighbors, the other tropæolums, to have the beautiful gift; but how can she send it to them?
She makes herself beautiful and bright; she fills her horn with honey and exhales fragrance.
The bees and the humming birds see her and approach. No doubt they rejoice in the bright colors, the perfume, and the nectar. They come on bright wings, and as they approach the nectary the grains of red pollen cling to them.
They cannot get enough nectar from one flower; each gives them a little, then they fly to others for more. From flower to flower they hasten and scatter pollen as they go. The pollen from one flower is often left in another, and this is what the tropæolum wants. It wishes its pollen to reach another flower, and uses the bees and the humming birds as its messengers.
Its stamens lie flat on the floor of the flower. When one is about to ripen its anther rises and stands up in front of the spur, where the nectar is ready. Then out bursts the fine red pollen. Only one anther ripens at a time. It sometimes takes several days for the tropæolum to shed all its pollen.
As soon as the pollen is gone the anther lies down again out of the way.
The stamens do not crowd the doorway of the spur; they lie down out of the way until they ripen, then they stand in front of the spur, and when their pollen is shed they lie down again.
They do not obstruct the way to the nectary because they wish the bees and birds to find an easy entrance.
Why does one anther ripen at a time? Why do not all shed pollen together, as is the habit of the morning-glory, and finish in one day?
Perhaps the tropæolum fears the rain may ruin the chances of the seeds to get pollen. We know that water spoils the pollen, and though the tropæolum has fringes to keep it from the nectary, and a roof to protect it, more or less would doubtless beat in during a hard shower.
Does the tropæolum bloom, then, in the rainy season in its own hot home—in the rainy season when the showers are terrific?
We should like to know that.
If it did, that would be a good reason for ripening the anthers one at a time. If one were spoiled, another might succeed.
We may be sure there is a good reason for this habit of the tropæolum, though we may not have discovered it.
When at last the pollen is gone and the anthers are empty and shriveled, the spur is still full of honey.
In front of it has risen, not a stamen this time, but a dainty five-rayed stigma. It is held in place by the style, and is ripe and ready for pollen. It has unfolded its five rays that it may catch and hold the pollen grains.
But all its pollen is gone! The bees and the birds have carried it away. The bees ate some and carried some home to their hives. None remains for the five-rayed stigma. But here comes a bee, a large, yellow-banded bumblebee. She has a ball of red pollen in each of her two baskets. She gathered it in another tropæolum blossom, and intends to take it home to feed the young bees; but as she enters our pollenless flower for nectar, lo! she brushes aside the five-rayed stigma. A few grains of pollen from her legs cling to the stigma, for it is sticky and holds them.
The bee hurries away. She does not know what she has done; she does not know that in brushing aside the stigma that stood in her way she has given life to the seeds and provided for a new generation of tropæolum vines.
The flower gave pollen to its neighbors, and now in its need they have sent pollen to it.
Soon the bright corolla fades and falls. Its work is done. It expressed its joy in life; it called the bees, and by them sent pollen to its neighbors, and took pollen from them in return.
For many days it kept its long red horn full of sweet nectar, until its stigma rose and took the pollen, when the flower faded and fell. But the five-rayed stigma did not fall. It remained attached to the green little fruit that lay hid in the heart of the flower.
It is not easy to see this fruit when the flower first opens, for it is small and hidden by the stamens.
But after the pollen has reached the stigma the fruit grows rapidly. The corolla falls, and the stem that holds the fruit curls up. It curls up until it has drawn the green fruit down under the leaves, out of the way of the buds that wish to open. The stigma and style fall off at last, and leave the fruit to ripen alone.
