One cause of extermination is easily grasped. Cypripeds have not the
power of fertilizing themselves, except a single species, _Cyp.
Schlimii_, which--accordingly, as we may say--is most difficult to
import and establish; moreover, it flowers so freely that the seedlings
are always weak. In all species the sexual apparatus is so constructed
that it cannot be impregnated by accident, and few insects can perform
the office. Dr. Hermann Muller studied _Cyp. calceolus_ assiduously in
this point of view. He observed only five species of insect which
fertilize it. _Cyp. calceolus_ has perfume and honey, but none of the
tropical species offer those attractions. Their colour is not showy. The
labellum proves to be rather a trap than a bait. Large insects which
creep into it and duly bear away the pollen masses, are caught and held
fast by that sticky substance when they try to escape through the
lateral passages, which smaller insects are too weak to force their way
through.
Natural hybrids occur so rarely, that their existence is commonly
denied. The assertion is not quite exact; but when we consider the
habits of the genus, it ceases to be extraordinary that Cypripeds
rarely cross in their wild state. Different species of Cattleya,
Odontoglots, and the rest live together on the same tree, side by side.
But those others dwell apart in the great majority of cases, each
species by itself, at a vast distance perhaps from its kindred.
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