color (Fig. 1). The rates of shoot-tip necrosis were also higher in the medium containing 440 mg L-1CaCl2.2H2O (21 and 51% for the first and second subculture, respectively) than in the shoots cultured in the presence of 1320 mg L-1CaCl2.2H2O (10 and 30% for the first and second subculture, respectively) (Table 1). The high relative humidity of the gaseous atmosphere is commonly observed in tissue culture vessels and this factor alone probably results in a substantialdepression of transpiration and creates conditions in which calcium related disorders might tend to develop in fast growing shoot tips (Abousalim and Mantell 1994). The absorption and the translocation of Ca through the plant tissues are dependent of the mass flow and it is limited by thelow transpiration of the explants cultivated in theflasks under high relative humidity, reducing the transport of ions of low mobility as the calcium (Sha et al. 1985). This symptom of shoot tip necrosis caused by calcium deficiency occurs in both ex vitro and in tissue culture (Sha et al. 1985; Piagnani et al. 1996).