Cohesion

Cohesion, (1) the tendency for closely united particles to resist separation. The forces that keep the molecules of a body close together only act through very small distances. That is to say, if two particles are to exert a cohesive force on each other, their distance apart must be exceedingly small. Cohesion may be well observed in a soap film, or in a drop of water hanging from a glass rod. In the latter case we have the weight of the drop supported by a small area of water-particles. The term adhesion is similarly applied to the tendency for particles of different kinds to resist separation when once they are brought into close contact; it is instanced by the attraction between the water-particles and glass rod, in the case of the pendant drop previously mentioned.

(2) In Botany, cohesion means the union of similar organs, e.g. sepals to sepals, stamens to stamens, etc. In the flower apparent cohesion of the sepals, petals, filaments, or carpels is generally due to the intercalary growth of a zone of tissue below the whorl of organs which appear to cohere, carrying them up with it, and forming the so-called calyx-tube, corolla-tube, staminal-tube, or syncarpous ovary. The united (syngenesious) anthers of Compositae are a case of true cohesion of originally distinct structures.