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It is the turn now of other lichens to colonize it. These may be the little trumpet or horn and cup lichens, _Cladonias_, or perhaps the larger grey kinds, _Parmelias_ and _Physcias_, which have leaf-like fronds and form circles of perhaps eight to ten inches in diameter. The crust-lichen is overgrown, broken up, disorganized, and devoured by the _Parmelias_ and _Cladonias_, who are helped by bacteria, insects, and animalcula which shelter below them. These leafy lichens grow much more rapidly.