oe ASCLEPIADACEAE. eral | 
PeriPpLoca. Silk Vine. 
(Family Asclepiadaceae). 
Soft-wooded twiners with milky 
sap: deciduous. Stems _ terete, 
moderate: pith round, excavated. 
Buds rather small, solitary, near- 
ly concealed by the _ leaf-bases. 
Leaf-scars opposite, raised, shriv- 
eled or elliptical with a single 
crescent-shaped bundle-trace:' sti- 
pule-scars lacking. 
Winter-characters of P. graeca 
are figured by Schneider, f. 109. 
Several herbaceous milkweeds 
are twining plants and become 
troublesome weeds when they get 
a foothold in orchards or beside 
fence-posts where it is hard to 
dislodge their strong perennial 
roots. The silk vine, which is the 
only woody representative of the 
family that is hardy well into the 
North, is a strong climber. 
A technical distinction between the closely related fami- 
lies Apocynaceae and Asclepiadaceae is found in the powdery 
or granular pollen of the former and the coherent pollinia of 
the latter, familiar to every student of milkweed pollination 
and to every close observer of bees and other insects, to which 
the pollen masses become attached. In Periploca these pol- 
linia are less firm than in most genera of the family. A 
typographic slip in one case has caused the apocynaceous pol- 
len to be called glandular, tempting one to parallel Engel- 
mann’s impatient exclamation when what he wrote for glu- 
tinous pollen appeared in type as gelatinous, “but who ever 
heard of gelatinous pollen?” 
Stems glabrescent from somewhat puberulent. P. graeca. 
