USE OF SOFT X-RADIOGRAPHY FOR EARLY NONDESTRUCTIVE DETECTION OF FLORAL DIFFERENTIATION IN DOUGLAS-FIR BUDS (PSEUDOTSUGA-MENZIESII (MIRB) FRANCE)

Weekly X-radiographs were made of Douglas fir buds on growing shoots a s a nondestructive method of detecting the onset of their meristem tra nsition from a vegetative to a floral state. The same procedure was fo llowed with sampled shoots to improve the interpretation of previous r adiographs made of whole branches on the tree. There was clear evidenc e of the floral state about 60 d after the beginning of the flower-pro moting treatment. Male and female cones were plainly distinguishable 7 5-80 d after the treatment. With this technique, it is possible to non -destructively follow the growth of floral primordia inside the buds. The technique can also be used to characterize bud samples on the basi s of more accurate criteria than those of external morphology. Good re sults were obtained on freeze-dried buds, particularly for showing vas cularization at the bud base.