1887] The Milkweeds. 615 
times four feet are entangled, and then ensues a struggle to 
escape. If strong enough, the fly tears itself away, but in the 
effort takes the pollinia attached to its feet along with it. “The 
basal appendages of each pair of pollen-masses,” says Mr. Smith, 
“are elastic, and when in the pouch they are like an extended 
spring, but the instant the masses are drawn out by the insect’s 
foot the spring closes, the two pollen-masses quickly cross each 
other and hold tightly on to the insect’s little claws.” The 
stigmas of the flower are exposed in the centre of the parts 
forming the apex of stamens and pistils, and these are not ripe 
at the same time as the pollen. It is therefore necessary for the 
pollinia to be withdrawn from the pouches and conveyed by the 
insect to another flower in which the stigmas are ripe before 
fertilization can take place. 
Other species of the family are noted for their medicinal 
properties. For example, one known as Tylophora asthmatica, 
or Indian Ipecacuanha, is largely used in cases of dysentery. 
Others are valued for their fibre. One of these is Calotropidis 
(Asclepias) gigantea, This is spun into the finest thread for 
sewing or weaving. Handkerchiefs made from it were shown 
in one of the Paris exhibitions. A species in our own country, 
very common in wet or damp places (Asclepias incarnata), pro- 
duces a long, tough fibre which could be used for many pur- 
poses. Another species (Marsdenia tenacissima) produces fibre 
so strong that the natives of some parts of India use it for bow- 
strings. The stems are dried in the sun, and the milky juice 
which exudes hardens into a substance like india-rubber; and 
_ there are other species in which this juice could be used for 
many of the purposes to which caoutchouc is now applied. 
It is thus seen that the family of Milkweeds is useful prac- 
tically, as well as interesting botanieally. We use the sap in 
our way as the plant uses it in its own. The same tough fibre 
which makes the plant disagreeable to animals the human race 
finds useful to itself. The same sweet-scented flowers which ` 
attract swarms of insects delight us in our greenhouses; and 
the same curious forms of stems adapted to a plant’s existence 
in dry and arid regions form curious features in the homes of 
civilized man. 
