610 . The Milkweeds. Dey 
on wih side of the slit the pollen-grains are found. The pe- 
culiar feature of these grains is that they are united into masses 
nye a masses 
Asclepias hanging 
twisted appendages 
and fastened to the 
gland above. 
or clusters, the individual grains 
held together by sticky threads, 
—a feature found in only one 
other family. The stigma sur- 
mounts the two ovaries like a 
7 ; Fic. 5. iora with hoods cut away 
large cap, and is placed imme- showing ovaries (0), the pollinia ( P 
and the m — (g) uniting two 
of the pollin 
arranged around the outside. To enable the pollen to reach the 
stigma the pollinium must be taken out of the sac where it hangs | 
and be inserted into the slit between the nectaries. This can only 
be effected through the agency of insects, and these perform the 
service in the following manner : 
The visitor, attracted by the odor, alights to suck the nectar a 
secreted in the hoods. In its progress over the blossom some 
one of the hairs of its legs is sure to slide into the slit between 
the hoods. Pursuing his way by drawing up his leg, the hair: 
will be guided by two flanges at the sides into the upper and 
narrower part of the slit, and there become fast. Feeling a de- 
tention, the captive will pull to release himself, and, if possessed 
of sufficient force, will bring out of the sacs at the sides two 
pear-shaped pollinia, each fastened to the lamina, or gland, by a 
short appendage (see figure). When they are first withdrawn 
the pollinia are divergent. In a comparatively short space of 
time the appendages begin to twist, and then the pollen-masses 
are brought close together; not, however, before the insect to — 
