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58 EUEGRGEN: Quercus suberNemwGRK10000 TI!,I1000 L ........ _ ... .ii1001I101IIio 5 10•........15QUAUTY INDEX20 25 30Fig. 4. Proportion (in %) of superiority in cork quality of the candidate trees withrespect to control trees. Mean superiority of the selected group: >300%.>-I-..Jco«Cl:«>o +--------+--------+--------+--------+--------+------~o 5 10 15 20 25 30QUALITY INDEXFig. 5. Variability expressed as standard deviation of the quality index for four trees ineach selected group. Mean variability of the population: >50%.It is also necessary to start the study of acorn quality. Before that, a suitablemethod of collecting has to be developed. Atfirst, it will focus on the selected plustrees but, in the future, a specific programme on acorn improvement may beconvenient.In conclusion it can be said that the first stage of the improvement pr'ograrnme -the selection of plus trees in La Almoraima - is nearly complete. The next step willbe to sample seeds or vegetative material from the selected trees in order topropagate them. This work must be accompanied with studies on heritability of