Abstract
CO2 absorption (PAT) and transpiration (E) rates, and leaf diffusion resistance (ri) were individually studied in all leaves of tobacco plants (Nicotiana tabacum L. cv. Wisconsin 38) before flowering. Differences between old, middle age and young leaves were in all characteristics studied and found statistically significant. In all three leaf age groups E was closely correlated to ri. No similar correlation was discovered between PN and ri. The highest ratiosP N /E in young and middle age leaves indicate that the increase of the internal resistance to photosynthesis with leaf age was more rapid than that of ri.