į 
1887] The Mülkweeds:  - 613 
The sixty or more species of Asclepias are, with two exceptions, 
confined to the American continent, and the amount of milk 
juice varies in the different species. The acridity of those species 
which have no milky juice is a sufficient protection, however, 
from the attacks of herbivorous animals. 
Other genera of the order present, in their turn, various fea- 
tures of interest. S/apelia is a genus of about one hundred 
species, all of them found in the Cape of Good Hope region. 
hey are peculiar in having thick, fleshy stems, generally with 
small scales in place of leaves borne on the angles of the stems. 
The flowers are mainly star-shaped, starting out at various points 
on the stem, and are remarkable for their disagreeable, carrion- 
like odor. This is so marked in certain species that it attracts 
large numbers of flies. These sometimes lay their eggs in the 
flowers, but the progeny, when hatched, die for want of food. 
The main object of the odor of the flower is to attract insects 
' for the purpose of fertilizing it by the transfer of pollen from 
one plant to another. About the centre of the flower are cer- 
tain black spots, which are peculiarly attractive to insects. In 
one species (S. asterias) flies have been observed to feed greedily 
about these spots, and it is found that the fly’s tongue often gets 
caught in a trap situated hereabouts. When thus caught it 
struggles violently to escape, and, if successful, goes away with 
a pair of pollinia attached to its tongue, drawn from their en- 
closing sacs. The apparatus which catches the tongue is a 
veritable spring-trap, closing with a snap on the intrusion of 
any disturbing object. The insect, laden with the pair of pollen- 
masses, flies to another flower, and there places them in a po- 
sition where the pollen-tubes can penetrate the stigma. Here, 
then, there are three interesting features to be noted,—first, the 
thick, succulent, leafless stems, which enable the plants to exist 
in dry, sandy soil, and, at the same time, furnish no inducement 
to any stray animal to feed upon; second, the carrion-scented 
- flowers, which attract flies, necessary for the fertilization of the 
stigma; and, third, a veritable spring-trap, which catches the 
tongue of the little carrier, so that it flies away with a aes 
to another flower, and effects cross-fertilization. 
The succulent stem may be regarded as developed because 
of the necessity to retain a supply of moisture in the dry, arid 
a mons, whither the E have probably. been driven from an 
