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The term vitrification is currently used to describe two types of processes related to tissue-cultured plant material. The first is used to describe organs and tissues having an abnormal morphological appearance and physiological function. The second is used to describe the transition from liquid to solid state, i.e. the formation of ice during low temperature storage of in vitro cultured cells, tissues and organs. Use of the same term to define two greatly different processes in the same research area can only lead to confusion, especially for key words. Thus it is appropriate to reconsider the usage of vitrification in the first sense mentioned above. It is recommended that the term vitrification should no longer be used to indicate plant material with an abnormal morphological appearance and physiological function, and should be substituted by the term 'hyperhydricity'.

Medium type, its water status and the relative humidity in the culture vessel modified carnation leaf development in vitro. Carnation shoot apices cultured on liquid or on 0.8% agar solidified media developed into plantlets having succulent and translucent leaves which are not transplantable to non-aseptic conditions. Increasing the agar and/or sucrose concentration in the medium as well as decreasing the relative humidity in the culture vessel by a desiccant promoted glaucous leaf production. Increased water status (4 I-I2O and relative humidity) increased shoot proliferation and translucency of leaves. Decreased water status reduced shoot proliferation but induced the formation of glaucous leaves. The culture of apices for 5-6 days on liquid medium prior to their subculture to 1.5% agar medium improved shoot proliferation and normal leaf development. An agar slant prevented the submergence of apices in water accumulating on the medium and thus reduced leaf translucency. Survival was further increased by the transfer of plantlets in uncapped culture vessels to a desiccator for 1 2 weeks prior to transplanting to soil.

Gladiolus bud explants propagated in agitated liquid medium, in the presence of the growth retardants daminozide, ancymidol, paclobutrazol or Majic, proliferated into massive bud aggregates without leaves. The buds developed into protocorms and after subculture to agar-solidified medium formed cormlets 8-10 mm in diameter. The corms were not dormant and, after transplanting to pots in the greenhouse, developed into plantlets, 5-6 months after explant isolation.

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