How Eucalypt fruits release their seed

Abstract

Living fruits are completely filled with seeds; and although partial dehiscence is usual in some species as soon as the fruit has matured, no seed is shed until the fruit died and the loculi have widened. The widening is accomplished by three mechanisms, illustrated respectively by E. regnans, E. globulus, and E. calophylla. In .E. regnans there is a thin, woody ovary wall which retracts well into the calyx tube. In E. globulus the loculi are surrounded by thick fleshy tissue which shrinks strongly when dried but remains adnate to the rigid exterior calyx tube. In E. calophylla the valves are also rather fleshy, but not adnate to the calyx tube; they shrink strongly in both longitudinal and centrifugal directions.

The above three mechanisms serve not only to widen but also to open the loculi. the case of fruits with strongly protruding valves, opening is aided by the outward bending of the valve tips (e.g. E. viminalis). The bending occurs because the dorsal layer of the valve consists of softer tissue which shrinks more strongly than the ventral layer.

The other species examined (E. simmondsii, E. urnigera, E. obliqua, E. delegatensis, E. coccifera, E. ficifolia, E. setosa, E. eximia, E. grandfilia, E. aspera, E. clavigera, E. tesselaris) all depend on one or more of the above mechanisms.