A versatile and inexpensive systém with a hand scanner was developed and evaluated for measuring leaf area. A BASIC programme was created for processing the image fíles and calculating the area of scanned objects. The accuracy was better than 1 % of the reference area and it fell only when the area/perimeter ratio was less than 0.3 or when the measured object size was smaller than 0.1 cm^.
The effect of heat stress (35 to 50 °C) on photosynthesis was investigated in heat tolerant (N 22) and heat sensitive (IR 8) cultivars of rice {Oryza sativa L.). The net photosynthetic rate showed greater thermal stability in N 22 than in IR 8. The relative dechne of the rate of whole chain electron transport and photosystem 2 (PS2) activity was more pronounced in IR 8 than N 22. In both cultivars photosystem (PSI) activity was stimulated by thermal treatment. Chlorophyll (Chl) a fluorescence transient arising ffom PS2 showed inhibition in both cultivars at 45 and 50 °C. Maximum fluorescence decreased more in IR 8 than in N 22 by high temperature treatment.