Three winter wheat varieties were planted in Tibet Plateau.The geometry of canopy and interception of photosynthetically active radiation(PAR) were measured.Effects of those factors on grain yield were discussed.The results,from a theoretical analysis and field measurements,indicate that,in Tibet Plateau,leaves of winter wheat were erect while those in plain regions not so.From flowering to harvest time,the leaf area duration (LAD) of Plateau field was about 2 times of that of plain field.In growing sea...