PHYSIOLOGICAL STUDY OF DOUBLE CROSS HYBRID CLONES OF WHITE POPLAR UNDER WATER STRESS INDEX ANALYSIS ON COMPREHENSIVE JUDGEMENT OF DROUGHT RESISTANCE ABILITY OF WHITE POPLAR HYBRID CLONES Phenological Variation of Larix kaempferi and Its Hybrid Clones and Early Selection INFLUENCE OF WATER STRESS ON THE ABILITIES TO MAINTAIN TURGOR AND ADJUST OSMOSIS IN SEEDLINGS OF HYBRID CLONES OF Populus tomentosa