0 the way plants or plant parts react to gravity (= the force that pulls objects towards planets) -- geotropizm
Darwin also drew attention to the similarities between animals and plants, e.g., sensitivity to touch (thigmotropism), light sensitivity (phototropism), and gravity (geotropism).
Germination of embryos was defined as extension and positive geotropism of the radicle.
It is this negative geotropism and positive phototactic behaviour which may distinguish ballooning lepidopterans from the primitive non-ballooning lineage.
The mygalomorphs that do balloon express a level of negative geotropism that is not expected to be present elsewhere in the lineage.
