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Vitrified shoots were produced in multiplication cultures of Castanea sativa Mill. when Murashige and Skoog mineral medium was used during successive subcultures, whereas normal shoots were obtained when Heller's macronutrient formula was used with or without addition of 1 mM (NH4)2SO4. Vitreous and normal plantlets were compared both anatomically and chemically. Xylem and sclerenchyma tissues are less differentiated and lignified in vitrified than in normal shoots. On the other hand, there is a hypertrophy in the cortical and pith parenchyma. Leaves of vitrified shoots are characterized by the lack of clear differentiation between the palisade and spongy mesophyll, where a system of large intercellular spaces develops. The cytohistological zonation of vitrified apices is characterized by the comparatively small meristem tissue in the apical dome. Phenolic content of explants, assayed by high pressure liquid chromatography, was lower in vitreous than in normal cultures. Gallic acid was identified in both types of cultures.

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In laboratory tests the allelopathic potential ofErica vagans, Calluna vulgaris, andDaboecia cantabrica was determined. Aqueous extracts of flowers ofD. cantabrica and leaves ofC. vulgaris inhibit root and hypocotyl growth of red clover, the former causing 51% inhibition of germination. Intact aerial parts of the Ericaceae here studied drastically reduced the growth of red clover and 100% inhibition of germination was caused by flowers ofD. cantabrica. Inhibition of aqueous extracts remains after Chromatographic separation, and two well-defined inhibition zones may be observed. Hydrosoluble organic compounds (phenol-like compounds) could probably be responsible for the inhibitions detected.

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