150
A. A L L S O P P
ciated with a greater rate of leaf formation, a relationship which is
clearly in accordance with the view that deeper lobing is promoted by
an increasing excess of carbohydrate. Njoku accepted this possibility,
but suggested another explanation in terms of specific growth substances
(see Section III,F,3). In experiments with Passiflora caerulea, Montaldi
et al. (1963a) found that plants grown with deficient mineral supply
never advanced beyond the 3-lobed leaf stage and sometimes even
reverted to the formation of simple leaves, whereas control plants with
adequate mineral nutrients produced the normal 5-lobed adult leaves
(Fig. 1). These results are evidently related to diminished strengthening
growth of the retarded plants.
There have been few studies of the effects of mineral nutrients on
the shoot apex. In an investigation of the effects of five different levels
of ammonium nitrate ranging from 0.0001 to 0.0048 M on the apical
meristems of 12 inbred lines and 9 hybrids of maize, Burkholder and
McVeigh (1940) found that with increase in the nitrogen level there
was a marked increase in size and differentiation of the apex. In rhizomes
of Dryopteris maintained without a mineral nutrient supply, Cutter
(1955) observed a progressive reduction in the size of the apical cone,
and a reversion of the phyllotaxis to a lower system characteristic of
the sporeling.
b. Effects of Carbohydrate Nutrition. Almost all studies on the effects
of carbohydrate nutrition on heteroblastic development in vascular plants
have been carried out on pteridophytes. Wetmore (1953, 1954) discovered
that, over a certain range, increases in sugar concentration promoted
heteroblastic leaf development in various fern sporelings. He suggested
that the mitotic processes of leaf formation are perhaps stimulated by
increased respiration with higher sugar concentrations, but as previously
pointed out (Allsopp, 1965b) his results are more readily explained in
terms of improved primary strengthening.
In investigations on Pteridium aquilinum, Gottlieb (1958) found that
sporelings growing in vitro quickly reverted to the production of relatively simple leaves when exposed to conditions leading to carbohydrate
starvation. In later work, Gottlieb and Steeves (1965) observed a striking and consistent relationship between the carbohydrate content of the
medium and the developmental stage attained by young sporelings.
The latter normally pass from an initial orthotropic stage, through a
transitional leaf-bearing plagiotropic rhizome stage, to a condition with
rapidly growing apparently leafless long shoots, and leafy lateral short
shoots. It was found that at concentrations of sucrose below 2%, leafbearing rhizomes were produced indefinitely, whereas at concentrations
from 4 to 8% the short shoot habit could be reliably stabilized. There
was also a close correlation between carbohydrate level and stelar
ontogeny.
A. A L L S O P P
ciated with a greater rate of leaf formation, a relationship which is
clearly in accordance with the view that deeper lobing is promoted by
an increasing excess of carbohydrate. Njoku accepted this possibility,
but suggested another explanation in terms of specific growth substances
(see Section III,F,3). In experiments with Passiflora caerulea, Montaldi
et al. (1963a) found that plants grown with deficient mineral supply
never advanced beyond the 3-lobed leaf stage and sometimes even
reverted to the formation of simple leaves, whereas control plants with
adequate mineral nutrients produced the normal 5-lobed adult leaves
(Fig. 1). These results are evidently related to diminished strengthening
growth of the retarded plants.
There have been few studies of the effects of mineral nutrients on
the shoot apex. In an investigation of the effects of five different levels
of ammonium nitrate ranging from 0.0001 to 0.0048 M on the apical
meristems of 12 inbred lines and 9 hybrids of maize, Burkholder and
McVeigh (1940) found that with increase in the nitrogen level there
was a marked increase in size and differentiation of the apex. In rhizomes
of Dryopteris maintained without a mineral nutrient supply, Cutter
(1955) observed a progressive reduction in the size of the apical cone,
and a reversion of the phyllotaxis to a lower system characteristic of
the sporeling.
b. Effects of Carbohydrate Nutrition. Almost all studies on the effects
of carbohydrate nutrition on heteroblastic development in vascular plants
have been carried out on pteridophytes. Wetmore (1953, 1954) discovered
that, over a certain range, increases in sugar concentration promoted
heteroblastic leaf development in various fern sporelings. He suggested
that the mitotic processes of leaf formation are perhaps stimulated by
increased respiration with higher sugar concentrations, but as previously
pointed out (Allsopp, 1965b) his results are more readily explained in
terms of improved primary strengthening.
In investigations on Pteridium aquilinum, Gottlieb (1958) found that
sporelings growing in vitro quickly reverted to the production of relatively simple leaves when exposed to conditions leading to carbohydrate
starvation. In later work, Gottlieb and Steeves (1965) observed a striking and consistent relationship between the carbohydrate content of the
medium and the developmental stage attained by young sporelings.
The latter normally pass from an initial orthotropic stage, through a
transitional leaf-bearing plagiotropic rhizome stage, to a condition with
rapidly growing apparently leafless long shoots, and leafy lateral short
shoots. It was found that at concentrations of sucrose below 2%, leafbearing rhizomes were produced indefinitely, whereas at concentrations
from 4 to 8% the short shoot habit could be reliably stabilized. There
was also a close correlation between carbohydrate level and stelar
ontogeny.