Anna B. Comstock

Iris in blossom. Photo by Verne Morton.

The Blue Flag, or Iris

Teacher's Story

The iris blossom has a strange appearance, and this is because nothing in it is as it seems. The style of the pistil is divided into three broad branches and they look like petals; and they have formed a conspiracy with the sepals to make a tunnel for bees, leaving the petals out of the plan entirely and the sepals "rise to the occasion." The petals stand up lonely between the three strangely matched pairs, and all they accomplish by their purple guiding lines, is to basely deceive the butterflies and other insects which are in the habit of looking for nectar at the center of a flower. If we look directly down into the flower of the blue flag, there are ridges on the broad styles and purple veins on the petals, all pointing plainly to the center of the flower, and any insect alighting there would naturally seek for nectar-wells where all these lines so plainly lead. But there is an "April fool" for the insects which trust to these guides, for there is no nectar to be had there. Dr. Needham, in his admirable study of this flower and its visitors (American Naturalist, May, 1900), tells us that he has seen the little butterflies called "skippers," the flag weevils and the flower beetles all made victims of this deceptive appearance; this is evidence that the nectar guiding lines on flowers are noted and followed by insects.

The blue flag is made for bees; the butterflies and beetles are interlopers and thieves at best. The bees are never deceived into seeking the nectar in the wrong place. They know to a certainty that the sepal with its purple and yellow tip and many guiding lines, although far from the center of the flower, is the sure path to the nectar. A bee alights on the lip of the sepal, presses forward scraping her back against the down-hanging stigma, then scrapes along the open anther which lies along the roof of the tunnel; and she here finds a pair of guiding lines each leading to a nectar-well at the very base of the sepal. The bees which Dr. Needham found doing the greatest work as pollen-carriers were small solitary bees (Clisodon terminalis and Osmia destructa);  each of these alighted with precision on the threshold of the side door, pushed its way in, got the nectar from both wells, came out and sought another side door speedily. One might ask why the bee in coming out did not deposit the pollen from its own anther upon the stigma; but the stigma avoids this by hanging down, like a flap to a tent, above the entrance, and its surface for receiving pollen is directed so that it gathers pollen from the entering bee and turns its back to the bee that is just making its exit.

The arrangement of the flower parts of the iris may be described briefly thus: three petals, three sepals, a style with three branches; the latter being broad and flat and covering the bases of the three sepals, making tubes which lead to the nectar; three anthers lie along the under side of the styles. The wild yellow iris is especially fitted for welcoming the bumblebee as a pollen-carrier, since the door between the style and the sepal is large enough to admit this larger insect. The bumblebees and the honey-bees work in the different varieties of iris in gardens.

In some varieties of iris there is a plush rug along the vestibule floor over which the bee passes to get the nectar. Through a lens, this plush is exquisite—the nap of white filaments standing up and tipped with brilliant yellow. Various theories as to the use of this plush have been advanced, the most plausible being that it is to keep the ants out; but the ant could easily pass along either side of it. While holding an iris in my hand, one day in the garden, a bumblebee visited it eagerly, never noting me; after she had probed the nectar-wells, she probed or nibbled among the plush, working it thoroughly on her way out. Was she a foolish bee, or did she find something there to eat? What child will find if other bees do this?

Method—While the blue flag is the most interesting of our wild species of iris, yet the flower-de-luce, or the garden iris, is quite as valuable for this lesson. The form of the flowers may be studied in the schoolroom, but the pupils should watch the visiting insects in the garden or field.

3. Where is the stigma? What is there very peculiar about the styles of the iris? Can a bee, when backing out from the side door, dust the stigma with the pollen she has just swept off? Why not? How does the stigma of the next flower that the bee visits get some of the pollen from her back?

4. Look straight down into an iris flower. Can you see the three petals? How are they marked? How would these lines on the petals mislead any insect that was searching for nectar?

5. Watch the insects visiting the iris. Do you know what they are? What do they do?

6. Describe the way the iris flower-bud is enfolded in bracts. What is there peculiar about the way the iris leaves join the stem?

7. How many kinds of flag, or iris, do you know?

8. Describe the seed-vessel and seeds of the iris.

Fleur-de-lis. Photo by Cyrus Crosby.