146
A. ALLSOPP
however, when the supported sporelings were transferred to 5% glucose
or 2% glucose + 3% mannitol, nor when land forms from 4 or 5%
glucose media were transferred to the 2% glucose + 3% mannitol media.
On the other hand, when sporelings were transferred to media of higher
concentration, e.g., from 1 or 2% glucose to 5 or 7.5% glucose, there
were no pronounced morphological changes.
j . Effects of Growth Substances on Land and Water Forms. The auxins
indoleacetic acid and naphthaleneacetic acid had no evident effect on the
land-water form relationship. Indoleacetonitrile, however, at its optimal
concentration of 10 mg/liter induced the development of water form
characteristics in sporelings in media with 4% glucose and 2% glucose
+ 2% mannitol, which resulted in the formation of land forms in the
absence of the nitrile (Allsopp, 1956). Similarly, addition of gibberellic
acid at 10 mg/liter brought about a transformation of land to water
forms when added to 4% glucose media. Kinetin had no evident effect
on this aspect of morphogenesis.
An unexpected result was the effect of certain inhibitors on the development of land forms. Arsenite at 0.05 mM and arsenate at 0.5 milf
promoted the development of land forms in 2% glucose media, in which
water forms normally develop. White (cited by Cutter, 1965) obtained
similar results with 2-thiouracil.
k. Discussion and Conclusions. The experimental results described
in Section III,A and B above enable certain conclusions to be drawn
with reference to heteroblastic development and the water-land form
relationship in Marsilea.
In the first place, it is certain that as concluded by Goebel (1898)
heteroblastic leaf development is closely controlled by the nutritional
status of the plant. The final quadrifoliate leaf form can be attained
only when sufficient nutrients are available; below that nutritional level
there is a retention of the simpler leaf forms or a reversion to such
leaves if quadrifoliate leaves have already been formed. Since either
carbohydrate or nitrogen supplies may be limiting it seems likely that
it is the rate of protein synthesis that controls the leaf segmentation,
particularly since the heteroblastic development is considerably affected
by various protein synthesis inhibitors.
It also seems certain that changes in the nutrient supply cannot
exert an immediate effect on leaf segmentation. However favorable the
nutrient level of the medium, Marsilea sporelings never form a quadrifoliate leaf at once; such a leaf is always preceded by simpler primary
leaves. Similarly the earlier lateral buds always begin their development
by the formation of simple leaves, even when the subtending leaf is
already quadrifoliate and when there can be no question of nutrient
deficiency (Allsopp, 1953a). It would therefore seem that whatever the
A. ALLSOPP
however, when the supported sporelings were transferred to 5% glucose
or 2% glucose + 3% mannitol, nor when land forms from 4 or 5%
glucose media were transferred to the 2% glucose + 3% mannitol media.
On the other hand, when sporelings were transferred to media of higher
concentration, e.g., from 1 or 2% glucose to 5 or 7.5% glucose, there
were no pronounced morphological changes.
j . Effects of Growth Substances on Land and Water Forms. The auxins
indoleacetic acid and naphthaleneacetic acid had no evident effect on the
land-water form relationship. Indoleacetonitrile, however, at its optimal
concentration of 10 mg/liter induced the development of water form
characteristics in sporelings in media with 4% glucose and 2% glucose
+ 2% mannitol, which resulted in the formation of land forms in the
absence of the nitrile (Allsopp, 1956). Similarly, addition of gibberellic
acid at 10 mg/liter brought about a transformation of land to water
forms when added to 4% glucose media. Kinetin had no evident effect
on this aspect of morphogenesis.
An unexpected result was the effect of certain inhibitors on the development of land forms. Arsenite at 0.05 mM and arsenate at 0.5 milf
promoted the development of land forms in 2% glucose media, in which
water forms normally develop. White (cited by Cutter, 1965) obtained
similar results with 2-thiouracil.
k. Discussion and Conclusions. The experimental results described
in Section III,A and B above enable certain conclusions to be drawn
with reference to heteroblastic development and the water-land form
relationship in Marsilea.
In the first place, it is certain that as concluded by Goebel (1898)
heteroblastic leaf development is closely controlled by the nutritional
status of the plant. The final quadrifoliate leaf form can be attained
only when sufficient nutrients are available; below that nutritional level
there is a retention of the simpler leaf forms or a reversion to such
leaves if quadrifoliate leaves have already been formed. Since either
carbohydrate or nitrogen supplies may be limiting it seems likely that
it is the rate of protein synthesis that controls the leaf segmentation,
particularly since the heteroblastic development is considerably affected
by various protein synthesis inhibitors.
It also seems certain that changes in the nutrient supply cannot
exert an immediate effect on leaf segmentation. However favorable the
nutrient level of the medium, Marsilea sporelings never form a quadrifoliate leaf at once; such a leaf is always preceded by simpler primary
leaves. Similarly the earlier lateral buds always begin their development
by the formation of simple leaves, even when the subtending leaf is
already quadrifoliate and when there can be no question of nutrient
deficiency (Allsopp, 1953a). It would therefore seem that whatever the