PART LY. | GENERAL RETROSPECT, 583 
of visitors, expose their pollen (but in that case their stigmas also) 
to short-lipped insects, which then act as subsidiary fertilising 
agents (cf. Composite, Silenee, A’sculus, Echiwm, Gnothera, Lonicera, 
etc.). And all flowers with hidden anthers have only been able to 
shelter their pollen from rain in so far as they have developed 
other adaptations for particular visitors, which compensate for the 
less general access of pollen-carrying insects. For this reason, 
flowers with hidden pollen afford us the most conspicuous ex- 
amples of adaptation in form and in dimensions to a more or 
less narrow circle of visitors (cf. Orchidew, Iris, Papilionacee, some 
Boraginee, Labiate, Scrophulariacee, Apocynee, Ericacew, etc.). 
These adaptations are always directly concerned in insuring self- 
fertilisation, and therefore fall to be considered in a future section. 
But the more perfectly flowers are adapted for cross-fertilisation 
by particular insects, the more unlikely does it become that other 
insects visiting the flowers will effect cross-fertilisation, and the more 
will such visits of other insects be useless or injurious to the plant. 
So concealment of the pollen is useful (to a subsidiary degree) in 
limiting insect-visits, and this effect has now to be considered. 
Concealment of the pollen in a cone of apposed anthers 
(Viola, Borago, Symphytum) hinders it from being devoured by 
flies and beetles, and renders it more difficult for bees to collect it; 
while honey-seeking bees cannot reach the honey without causing 
the cone to open and shed its pollen on them. 
Concealment of the anthers within open tubes (I/yosctis, Vinca, 
Syringa, etc.) renders it more difficult for beetles to devour the 
pollen, and for bees to collect it; but if the tube is wide enough 
-(Syringa), the more highly developed proboscides of certain Syrphide 
can enter and obtain the pollen, while narrower tubes (J/yosotis, 
Vinca) prevent all Diptera from feeding on the pollen, and only 
permit their visitors to obtain honey. When the tube containing 
the stamens is closed (Anchusa, Linaria, Antirrhinum), all insects 
except bees, Lepidoptera, and some very minute intruders are shut 
out both from the honey and from the pollen. Pendulous flowers 
with included stamens and not too wide tubes protect their honey 
from removal by flies (Asparagus, Convallaria) or by other insects 
also (Erica, Vaccinium) ; such flowers are therefore visited mainly 
or exclusively by honey-seeking insects. A vaulted structure 
sheltering the anthers from rain (/ris, most Labiates), does not 
“prevent, but to a great extent restricts, the theft of pollen by 
insects ; beetles are quite unable to obtain pollen so concealed, 
only a few of the more intelligent flies, especially Rhingia, and 
