Late 19th century; earliest use found in Journal of the Royal Microscopical Society. From photo- + -tropy; in sense 1 probably after phototropic; compare also German Phototropie.
Definition of phototropy in US English:
phototropy
nounfəʊˈtɒtrəpi
1Biology= "phototropism". Now rare.
2Chemistry= "photochromism".
Origin
Late 19th century; earliest use found in Journal of the Royal Microscopical Society. From photo- + -tropy; in sense 1 probably after phototropic; compare also German Phototropie.