Open main menu

Page:Popular Science Monthly Volume 49.djvu/708

This page has been proofread, but needs to be validated.

by a large and miscellaneous company, it can be fertilized apparently only by bees and perhaps by a few large flies.

The milkweed is a peculiarly constructed and very highly organized flower. The petals, five in number, fold back as soon as the blossom opens and press their backs against the flower stalk. Inside them, standing upright in a ring, are five honey jars, or nectaries, of peculiar form. Each nectary is hooded, and inside each is an incurved horn. Within the circle of honey jars are the five stamens, which are fixed to the base of the corolla, and stand in contact with each other, surrounding and inclosing the pistil. On top of the ring of stamens is a large five-sided disk, which keeps the pollen from being blown away, or wet with rain or dew. The whole stamen system is like a little tub or firkin, standing in the midst of the flower, upside down. Inside this firkin are two green pistils, which will be two green pods. The pollen of each anther is collected into an Indian-club-shaped mass, which is fastened to a similar mass formed by the pollen of the next anther. Thus the two connected pollen masses belong to two separate stamens. They are united by a tiny black disk. This disk is set just above an opening between the stamens which runs "clear through" to the pistil inside the firkin. The fly or bee stands on the outside of the firkin, and, tramping about there, gets her foot caught on the black disk—which is glutinous—and pulls out (if she is strong enough) the whole affair, disk and attached pollen masses. A bee will gather three or four of these at once, and I have seen one buzzing away from a head of milkweed loaded with no fewer than nine. Thus encumbered, she was for a moment held prisoner by the flower, unable to pull herself and her burden loose. Following the custom of bees, she carried the pollen masses at once to another milkweed plant, and perched upon one of its flowers in exactly the position in which she had stood when visiting the first. This brought the pollen masses on her feet exactly into the slits running through the stamen ring to the pistil.

The bee seems the favorite guest of the milkweed. The pollen masses come out at once at her tread, and are carried directly to the pistil of another flower.

Wasps visit the milkweed for its honey, but I have never seen them withdraw the pollen masses. Flies seldom do, though the flower is visited by flies of many species. Indeed, it is a general favorite, standing in the midst of a winged throng till dark, for twilight brings to it a number of small, dark-colored moths with very long proboscides.

But not all these visitors are permitted to go in peace. A small fly with his legs stuck to the black disks is frequently unable to pull himself loose after he has drunk his fill. On a bunch of