_Asclepias syriaca (A. cornuti)_
_Flowers_--Dull, pale greenish purple pink, or brownish pink, borne on
pedicels, in many flowered, broad umbels. Calyx inferior, 5-parted;
corolla deeply 5-cleft, the segments turned backward. Above them an
erect, 5-parted crown, each part called a hood, containing a nectary,
and with a tooth on either side, and an incurved horn projecting from
within. Behind the crown the short, stout stamens, united by their
filaments in a tube, are inserted on the corolla. Broad anthers united
around a thick column of pistils terminating hi a large, sticky,
5-angled disk. The anther sacs tipped with a winged membrane; a waxy,
pear-shaped pollen-mass in each sac connected with the stigma in pairs
or fours by a dark gland, and suspended by a stalk like a pair of
saddle-bags. _Stem:_ Stout, leafy, usually unbranched, 3 to 5 ft. high,
juice milky. _Leaves:_ Opposite, oblong, entire-edged smooth above,
hairy below, 4 to 9 in. long. _Fruit:_ 2 thick, warty pods, usually only
one filled with compressed seeds attached to tufts of silky, white,
fluffy hairs.
_Preferred Habitat_--Fields and waste places, roadsides.
_Flowering Season_--June-September.
_Distribution_--New Brunswick, far westward and southward to North
Carolina and Kansas.
After the orchids, no flowers show greater executive ability, none have
adopted more ingenious methods of compelling insects to work for them
than the milkweeds. Wonderfully have they perfected their mechanism in
every part until no member of the family even attempts to fertilize
itself; hence their triumphal, vigorous march around the earth, the
tribe numbering more than nineteen hundred species located chiefly in
those tropical and warm temperate regions that teem with the insects
whose cooperation they seek.
Commonest of all with us is this rank weed, which possesses the dignity
of a rubber plant. Much more attractive to human eyes, at least, than
the dull, pale, brownish-pink umbels of flowers are its exquisite silky
seed-tufts. But not so with insects. Knowing that the slightly fragrant
blossoms are rich in nectar, bees, wasps, flies, beetles, and
butterflies come to feast. Now, the visitor finding his alighting place
slippery, his feet claw about in all directions to secure a hold, just
as it was planned they should; for in his struggles some of his feet
must get caught in the fine little clefts at the base of the flower. His
efforts to extricate his foot only draw it into a slot at the end of
which lies a little dark-brown body. In a newly-opened flower five of
these little bodies may be seen between the horns of the crown, at equal
distances around it. This tiny brown excrescence is hard and horny, with
a notch in its face. It is continuous with and forms the end of the slot
in which the visitor’s foot is caught. Into this he must draw his foot
or claw, and finding it rather tightly held, must give a vigorous jerk
to get it free. Attached to either side of the little horny piece is a
flattened yellow pollen-mass, and so away he flies with a pair of these
pollinia, that look like tiny saddle-bags, dangling from his feet. One
might think that such rough handling as many insects must submit to from
flowers would discourage them from making any more visits; but the
desire for food is a mighty passion. While the insect is flying off to
another blossom, the stalk to which the saddle-bags are attached twists
until it brings them together, that, when his feet get caught in other
slots, they may be in the position to get broken off in his struggles
for freedom precisely where they will fertilize the stigmatic chambers.
Now the visitor flies away with the stalks alone sticking to his claws.
Bumblebees and hive-bees have been caught with a dozen pollen-masses
dangling from a single foot. Outrageous imposition!
Better than any written description of the milkweed blossom’s mechanism
is a simple experiment. If you have neither time nor patience to sit in
the hot sun, magnifying-glass in hand, and watch for an unwary insect to
get caught, take an ordinary house-fly, and hold it by the wings so that
it may claw at one of the newly-opened flowers from which no pollinia
have been removed. It tries frantically to hold on, and with a little
direction it may be led to catch its claws in the slots of the flower.
Now pull it gently away, and you will find a pair of saddle-bags slung
over his foot by a slender curved stalk. If you are rarely skilful, you
may induce your fly to withdraw the pollinia from all five slots on as
many of his feet. And they are not to be thrown or scraped off, let the
fly try as hard as he pleases. You may now invite the fly to take a
walk on another flower in which he will probably leave one or more
pollinia in its stigmatic cavities.
Doctor Kerner thought the milky juice in milkweed plants, especially
abundant in the uppermost leaves and stems, serves to protect the
flowers from useless crawling pilferers. He once started a number of
ants to climb up a milky stalk. When they neared the summit, he noticed
that at each movement the terminal hooks of their feet cut through the
tender epiderm, and from the little clefts the milky juice began to
flow, bedraggling their feet and the hind part of then-bodies. “The ants
were much impeded in their movements,” he writes, “and in order to rid
themselves of the annoyance, drew their feet through their mouths....
Their movements, however, which accompanied these efforts, simply
resulted in making fresh fissures and fresh discharges of milky juice,
so that the position of the ants became each moment worse and worse.
Many escaped by getting to the edge of a leaf and dropping to the
ground. Others tried this method of escape too late, for the air soon
hardened the milky juice into a tough brown substance, and after this,
all the strugglings of the ants to free themselves from the viscid
matter were in vain.” Nature’s methods of preserving a flower’s nectar
for the insects that are especially adapted to fertilize it, and of
punishing all useless intruders, often shock us; yet justice is ever
stern, ever kind in the largest sense.
If the asclepias really do kill some insects with their juice, others
doubtless owe their lives to it. Among the “protected” insects are the
milkweed butterflies and their caterpillars, which are provided with
secretions that are distasteful to birds and predaceous insects. “These
acrid secretions are probably due to the character of the plants upon
which the caterpillars feed,” says Doctor Holland, in his beautiful and
invaluable “Butterfly Book.” “Enjoying on this account immunity from
attack, they have all, in the process of time, been mimicked by species
in other genera which have not the same immunity.” “One cannot stay long
around a patch of milkweeds without seeing the monarch butterfly
(_Anosia plexippus_), that splendid, bright, reddish-brown winged
fellow, the borders and veins broadly black, with two rows of white
spots on the outer borders and two rows of pale spots across the tip of
the fore wings. There is a black scent-pouch on the hind wings. The
caterpillar, which is bright yellow or greenish yellow, banded with
shining black, is furnished with black fleshy ‘horns’ fore and aft.”
Like the dandelion, thistle, and other triumphant strugglers for
survival, the milkweed sends its offspring adrift on the winds to found
fresh colonies afar. Children delight in making pompons for their hats
by removing the silky seed-tufts from pods before they burst, and
winding them, one by one, on slender stems with fine thread. Hung in the
sunshine, how charmingly fluffy and soft they dry!
* * * * *
Among the comparatively few butterfly flowers--although, of course,
other insects not adapted to them are visitors--is the Purple Milkweed
(_A. purpurasceus_), whose deep magenta umbels are so conspicuous
through the summer months. Humming birds occasionally seek it, too. From
eastern Massachusetts to Virginia, and westward to the Mississippi, or
beyond, it is to be found in dry fields, woods, and thickets.