We carried out two types of experiments to clarify the emergence of ti
llers of rice plants under deep water conditions. One (Exp. 1) was to
keep the water level constant during the treatment, and the other (Exp
. 2) was to raise the water depth in some grades. In Exp. 1, when the
water level was deep enough to submerge the leaf sheath of the fully e
xpanded leaf of main stem at about 5.0 plant age in leaf number, the e
mergence of 3 rd node tiller (T3), which was growing inside the comple
tely submerged leaf sheath, was inhibited. Though the emergence of T 3
was inhibited, the emergence of T 4 and T 5, which were growing insid
e the completely submerged leaf sheath at the start of treatment, was
not inhibited. There was not always a relation between the inhibition
of tiller emergence and the complete submergence of the leaf sheath. I
n Exp. 2, the emergence of T 4, T 5 and T 6 node tiller was inhibited
when the water level was deep enough to submerge the leaf sheath of th
e fully expanded leaf of the main stem from the plant age of about 5.2
to 10.5 in succession. From the relation between the plant age at the
time of the deep water treatment and the growth response to the tille
r, we concluded that the growth response of the tiller under deep wate
r varied with the growth stage of the tiller bud; the most sensitive g
rowth stage of the tiller bud to the deep water was just before emerge
nce of the tiller which had four differentiated leaves. However, at th
e early growth stage just as the tiller bud differentiated 2-3 leaves
and at the late growth stage just as the tiller began to emerge from t
he leaf sheath, the tiller growth was scarcely inhibited.