Measurement of patterns of distribution of carbon-14-labelled assimilates in shoots of seedling and adult plants of Pinus radiata show that girdling the shoot increases the proportion of radioactive photosynthates that accumulate at the site of root initiation, compared with accumulation in non-girdled plants. Treatment of the base of the girdled shoot with indole butyric acid adds to this effect. The results support a belief that the success of air-layering as a technique for propagating plants is in part due to accumulation of photosynthates and auxins within girdled shoots as a result of interrupted phloem transport. The synthetic auxin, indole butyric acid, modifies patterns of photosynthate distribution and it is presumed that endogenous auxins act similarly.