Abstract：In order to clarify morphological characteristic in the floral bud differentiation process of Welsh
onion（Allium fistulosum L. var. giganteum Makino），this study took easy bolting variety‘Liaocong No.5’ and
tolerant bolting variety ‘Tianguangyiben’ as test material；conducted artificial low-temperature vernalization
at seedling stage；observed the floral differentiation process and changes of morphological characteristic in
green Welsh onion by anatomical lens；and divided the period of floral bud differentiation．The results showed
that the floral bud differentiation process and changes in morphological characteristic of these 2 Welsh onion
varieties with different bolting ways were basically the same．They could be classified into 4 phases including
induction stage，initial stage of flower bud differentiation，inflorescence and flower primordium differentiation
stage，flower organ differentiation stage．Plant transformed from nutrional growth to reproductive growth
when vegetative growth cone turned into a central convex ring form，might being considered as the initial
sign of the floral bud differentiation of Welsh onion．The closure or impending closure of the involucral
bracts was considered as signs for beginning of the inflorescence and flower primordium differentiation
stage．When the flower stem extended to 5-10 mm，an oblate outer peripheral primordium and a spherical
outer stamen primordium formed at the apex of each triangle flower primordium on the upper part of the
inflorescence axis，marking the initiation of flower organ differentiation．Floral organ differentiation entered
into late stage when 30% top florets opened after involucral cracking．There were larger differences between the
induction durations of‘Liaocong No.5 ’and ‘Tianguangyiben’，by 20 days and 35 days，respectively．The
duration of initial flower bud differentiation，inflorescence primordia and floral primordia differentiation，floral
organ differentiation were similar，being 10 days，15 days，and 30 days，respectively．
