arbuscle

1. (botany) A plant midway in height between a shrub and a tree; a dwarf tree.Examples: "Gumme is an Arabick word, and when it is put abſolutely; it muſt be underſtood of Gum-Arabick, which Galen calls Thebane, ſome Babylonian, and others Acanthine Gumme. It flowes from a certain arbuſcle, which [Pedanius] Dioſcorides calls Acacia, whereof he conſtitutes two ſorts […]"; "Ar′boret or arbus′cle. A little tree."; "Hybrid 800 was an arbuscle only 1.5 m in height at the age of six years because of suppression by adjoining poplars and honeylocusts. […] Further observations have shown that plants subjected to summer pruning when young suffered little from frosts. They continued to grow as arbuscles and no longer needed summer pruning. Some are now no less winterhardy than the most winterhardy specimens."

2. (mycology) A branched hypha in some fungi.Examples: "The hyphae of the arbuscle, which are finely ramified and form a floccose mass, soon lose their individuality and make a structureless granular and gummy conglomeration […]"

3. (mycology) The site at which a symbiotic fungus attaches to the roots of a plant and exchanges nutrients, etc., with it.Examples: "Detailed view of a typical fine endophyte arbuscle in the inner cortex. Note the well preserved structural integrity of the endophyte and the characteristic bifurcate hyphae […]. Infection was with the fine endophyte Glomus tenuis […]."; "The arbuscle formation increases the metabolic activity of the host cell which is mainly due to the bidirectional transfer of metabolites and nutrients to and from the fungus. Arbuscles live for only 4–15 days. They degenerate and are digested by the host cell […]."; "Enhanced fluorochrome accessibility, increased nuclease sensitivity and chromatin dispersion reflects an increase in chromatin decondensation which is a sign of greater transcriptional activity of the plant genome in arbuscle containing cells […]. The branching progression of the fungus into the host cell provokes de novo synthesis of the periarbuscular membrane. The periarbuscular membrane derived from the peripheral plasma membrane completely surrounds the arbuscle."

4. (zoology) A clump of feather-like cilia (hairlike structures).