Abstract
The factors which inhibit seed germination in leucaena (Leucaena leucocephala (Lam.) de Wit) were investigated in the 'giant type' ('K8' and 'K67'), the 'medium size type' ('K500') and the 'shrubby type ('K63’). Initially, seed structures and seed structure status were identified by using the scanning electron microscope, and later studied under the light microscope. By differential sealing of these structures, it was determined that the pleurogram was the structure through which water uptake occurred during imbibition. In hard seed the pleurogram was closed, but hot water treatments open the structure to permit water uptake. Scarification experiments were performed with the giant types and medium size 'K500 leucaena. The treatments consisted of immersion of the seed in 100 C water for periods up to 120 sec. 'K8 required 15 sec in boiling water to give > 95% germination, whereas in 'K67' 5 sec immersion resulted in 100% germination, and 'K500' required 20 sec for 98% germination. The most practical method of scarification, however, was suggested by the results that > 92% germination was obtained in the three types by placing them in boiling water which was allowed to cool to room temperature. The response of 'K63' to this treatment varied with the location of the seed source, although an average of > 85% germination was obtained by this treatment in seed from all sources.
