In botany, with the term casmogamy, coming from the Greek χάσμη “opening” and γάμος “wedding”, it is the phenomenon of the opening of the flowers that makes possible their pollination and consequent cross fertilization (allogamia, staurogamy).
In some rare cases in which the flowers remain closed (as in cleistogamy) the fertilization can only be direct (autogamy).
Casmogamy responds to the fundamental law of biology that cross breeding offspring is in all respects better than direct breeding offspring; the flowers that in most cases are hermaphrodites open to allow the pollen-carrying agents (wind, animals, etc.) to perform their function, and in the case of zoophilic pollination, the casmogamous flowers attract the attention of pollen-borne animals with their showiness, with the colors they show off, with the smells they emanate (vexillary or recall function).
In some cases, however, when plants bearing casmogamous flowers and cleistogamous flowers occur exceptionally, the latter produce better and more abundant seeds.