RiologiralJoumal ofthe Linnean Society. 1 3 : 155- 166. With 3 ligures
March 1980
Experimental manipulation of patterns of
resource allocation in the growth cycle
and reproduction of Smyrnium olusatrum L.
J. LOVETTDOUST*
School ofPlant Biology, U . C . N .W., Bangor, Gwynedd, Wales
Accepted/orpublication October I979
Plants of the monocarpic (normally biennial) Srnymrurn olusatrurn (Umbelliferae)were grown in pots
in soil at a high or low nutrient regime. Some plants receiving full nutrients were grown in a heated
glasshouse with 16 h days. The remainder were grown without supplementary lighting o r heat and
included control plants and others which received surgical treatment after ten months growth:
deradication (removal of half of the root stock); defoliation; deradication and defoliation. The
distribution ofplant biomass and of phosphorus were analyzed at the time of seed set.
Patterns of allocation of dry matter and phosphorus were quite different and were significantly
altered by treatments, which produced a range of allocation to reproductive structures ranging from
21 to 74%oftotalphosphorusand 12 to M%ofdrymatter.
Distribution patterns of total phosphorus are discussed in terms of the potential demands being
made by alternative structures and functions over the life cycle of the plants.
CONTENTS
Introduction
,
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Materials and methods
Results
. , , ,
Discussion
. . ,
Acknowledgements
References
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16.5
INTRODUCTION
In a previous paper (Lovett Doust, 1980) it was shown that plants of Smyrnium
olusatrum from three field sites differed in their patterns of biomass allocation
among organs. The internal resource economy of plants has, with very few
exceptions, been considered only with respect to biomass, essentially in a
‘currency’ of carbon or energy. However, the ecological implications of plant
growth patterns in relation to the accumulation and distribution of nutrients have
yet to be considered, and many of the questions about resource allocation
originally posed by Harper (1967) and partially answered for carbon (Harper,
1977 ) might usefully be asked with respect to the partitioning of other resources.
The distribution of phosphorus may be particularly important because it is known
to be concentrated in seeds and is vital in reporduction. The previous study had
* Present address: Department of Botany, University of British Columbia, Vancouver, B.C., Canada V6T 2B1
0024-4066/80/020 155- 12/$02.00/0
155
@ 1980 The Linnean Society of London
I56
J . LOVETT DOLIST
shown that, at the time of fruit set in S. olusatrum, 31.5% of the total biomass
including 59%of the total phosphorus is allocated to reproductive organs (Lovett
Doust, 1980).
Gregory (1953) has shown that, in the developing cereal plant, over 90%of the
phosphorus (and nitrogen) is accumulated before the plant has made 25% of its
growth in dry weight. This store of accumulated nutrient is the reserve upon
which later growth and development depend, and its level determines the final
yield. Smyrnium olusatrum is a semelparous species (biennial or longer-lived) and
has a longer period than the annual cereals in which to capture the nutrients that
are ultimately allocated at flowering and seed set. A series of treatments was
applied to plants of S. olusatrum in experiments that were designed to severely
alter sourcehink relationships within the plants.
MATERIALS AND METHODS
Seed of S. olusatrum was sampled from a single plant, collected at Glanrafon,
Bangor and the plants were grown individually in urpose-built pots (50 cm high
x 20 cm diameter) made of asphalt paper a n 8 lined with perforated black
polythene bags filled with John Innes Compost (No. 3) (except for treatment 6,
see below). The experiment was started in January 1976 and ran for approximately 550 days, until July 1977. Twenty plants were grown for each of six
treatments. The plants in Treatments 1 to 5 received liquid nutrient (‘Vita-Feed’)
every week in the second year of growth. Plants for Treatment 6 were germinated
and grown in a 5050 mixture of washed sand and John Innes Compost No. 3,
and did not receive weekly watering with liquid nutrient. Harvest 1 consisted of
five plants taken from each treament in mid-November 1976, i.e., at the end of
the first year of growth. At about the same time various defoliation and
deradication treatments were applied to the remaining plants. Harvest 2 was made
in July 197 7 and consisted of the remaining 15 plants per group, whether flowering
of not. The plants that flowered bore ripe mericarps at this stage.
Treatments were as follows :
Treatment I . Defoliation: the lamina was removed from basal leaves and from
the cauline leaves as and when they appeared.
Treatment 2. Deradication: the lower half of the root stock which had
developed in the first 10 months was removed; a water displacement technique
was used to ensure that as exactly as possible 50% of the root system was
removed. The cut surface was washed in a solution of ‘Benylate’ to protect
against fungal attack and the plants were repotted.
Treatment3.Both Deradication and Defoliation treatments were applied.
Treatment 4. Control: no treatments were applied.
Treatment 5 . Plants were grown as the controls but in a heated glasshouse with
16 h day length.
Treatment 6 . Low soil nutrient: the plants were germinated and grown in a
5 0 5 0 mixture of washed sand and John Innes Compost No. 3 and did not
receive the weekly watering with ‘Vita-Feed’.
All plants except those in treatment 5 were grown in a coldframe house with
no supplementary lighting or heat. Pots were arranged in a randomized design.
At both harvests plants were washed and separated into component organs,
dried and then weighed. The dried organs were then milled and subsamples were
RESOURCE ALLOCATION IN SMYRNIUM OL(ISATR1IM
157
ashed. Total phosphorus content was estimated using the molybdate-blue
method described in Allen (1974).
R ES CJ LTS
Approximately two-thirds of the plants in all treatment groups flowered. Two
of the plants died early in the low nutrient treatment and there was precocious
death at flowering time of several of the plants which had been both deradicated
and defoliated. Harvest 1 was taken a month after the experimental plants had
been deradicated or defoliated and at this harvest there was very little difference
in mean dry weight per plant (Table 1), The most spectacular effects of treatment
appeared at Harvest 2 as a five-fold range of weight of the flowering plants,
varying from 52 g in the deradicated-defoliated group (this included the weight
of tissues removed) to 275 g in control plants (Table 1). Deradication had
surprisingly little effect on the weight of flowering plants though it depressed by
about 80% the weight of those plants that remained vegetative. Defoliation
drastically reduced the dry weight of plants at the second harvest and these plants
added little extra dry matter during their second season of growth. Plants that
had been both deradicated and defoliated did not increase their total dry matter
beyond that present at Harvest 1. Plants in the low nutrient regime and those
grown in the heated glasshouse accumulated very little dry matter in year 2 and
the yield per plant was no greater than that of defoliated individuals. Plants
grown in a heated glasshouse, like the control plants, achieved a greater dry
weight if they remained vegetative.
The effect of treatments on phosphorus content was considerably less marked
than that on plant dry weight (Table 2). The mean total phosphorus per plant at
flowering was reduced by about 25% in plants that had been deradicated and by
50% in plants that were defoliated. At Harvest 2, plants in almost all treatment
groups contained less phosphorus than the control plants at Harvest 1.
The fraction of total biomass represented in reproductive tissue was 35% but
the very high value of 68 to 74% of total plant phosphorus was present in
reproductive tissues, in both the control and deradicated plants (Figs 1, 2). After
defoliation (with or without deradication) and in the low nutrient and heated
Table 1. Mean (kS.E.) total dry weight per plant (g) in vegetative and flowering
plants (totals are calculated to include tissue which had been removed
experimentally)
Control
Harvest 1
Vegetative
plants
Harvest 2
Vegetative
plants
Harvest 2
Flowering
plants
Deradicated
Defoliated
Deradicated
and
Defoliated
Low
nutrient
Heated
glasshouse
74.5(10.1)
59.0(11.31
56.0(9.9)
52.8(9.2)
51.1 (9.3)
55.3 (8.9)
337. (15.5)
247.5 (17.6)
34.2 (5.6)
37.4 (4.9)
58.0 (7.5)
105.7 (7.9)
276.7 (17.6)
266.8 ( 9.3)
72.6 (9.9)
52.4 (2.3)
70.6 (2.9)
62.4 (2.4)
1. LOVETT DOUST
158
Table 2. Mean (+ S.E.) total phosphorus per plant (g)in vegetative and flowering
plants (totals are calculated to include tissue which had been removed
experimentally)
Control
Deradicated
Defoliated
Deradicated
and
Defoliated
Low
nutrient
Heated
glasshouse
~
Harvest 1
Vegetative
plants
Harvest 2
Vegrtative
plants
Harvest 2
Flowering
plants
0.230(0.033) 0.1 14 (0.021)
0.136(0.027) 0.089(0.022) 0.100(0.018) 0.190(0.018)
0.485 (0.088) 0.378(0.031)
0.140 (0.023) 0.092(0.016) 0.115 (0.017) 0.375(0.022)
0.546(0.046) 0.405 (0.008) 0.253(0.031) 0.219(0.009) 0.178(0.007) 0.158 (0.005)
glasshouse regimes, very much lower fractions of total phosphorus were
allocated to reproductive structures and a much greater fraction was retained in
the tuberous root system or, in the plants grown in the heated glasshouse, was
present as dead leaf. In the defoliated treatments (with or without deradication) a
much increased proportion of plant phosphorus was held in peduncles. In plants
that were both deradicated and defoliated the allocation pattern of phosphorus
was changed dramatically and much more phosphorus was retained in the root
system and much less allocated to reproductive organs. Plants receiving this
treatment weighed only a fifth as much as control plants.
One of the most striking effects of treatment is to be seen in root: shoot ratios
(Fig. 3). Whereas it was not surprising to find that deradication and defoliation
disturbed this ratio, the greatly increased ratio of root: shoot in the plants grown at
low nutrient regime contrasts very strongly with that of control plnats and those
grown in the heated glasshouse.
Table 3 illustrates the changes in the concentration of phosphorus in different
organs of the plant. The concentration within fruits remained relatively invariant
except for the very low value for plants grow in the heated glasshouse. However,
the concentration in the rays of the inflorescence was greatly increased by
defoliation, low nutrient supply or growth in the heated glasshouse. The variations
in concentration in the rays are paralleled by variations in peduncles and the
inference is that the phosphorus was not actively translocated out of the peduncles
under these conditions.
The concentration of phosphorus in dead leaves may perhaps be taken as a
measure of the ability of the remainder of the plant to extract a vital nutrient and
transport it to sinks elsewhere. In the heated glasshouse the rate of leaf turnover
was very high and the leaves died with relatively high phosphate concentrations
in them (Table 3). On the control plants, leaves that died in the first year
contained high phosphorus concentrations but at the second harvest dead leaves
had, like the peduncles, been greatly reduced in phosphorus concentration.
Deradicated plants appeared also to be ‘efficient’ in depleting dying leaves of
phosphate but on plants that had been both deradicated and defoliated leaves
died with a concentration of phosphate higher than 3 mg/g (cf. 0.96 mg/g in dead
leaves of control plants). Concentrations of phosphorus in the tuberous roots
RESOURCE ALLOCATION IN SMYRNIUM OLUSATRUM
Control
159
Deradiccte
Defoliate
Derodicate and defoliate
Low nutrient
Heated qlasshouse
Figure 1 . The patterns of allocation of dry matter in flowering plants at the time of ripe fruit
(calculated excluding any excised tissue).
varied very greatly with treatments and the level of root phosphorus was
generally reduced to its lowest value in flowering plants. The only strong
exception to this rule was that plants that had been both deradicated and
defoliated retained a high concentration of phosphorus within the roots.
The concentration of phosphorus in stems fell to very low values in control
J . LOVETT DOUST
I60
Control
Defoliate
Low nutrient
Deradicate
Oeradicate and defoliate
Heoted glasshouse
Figure 2. The patterns of allocation of total phosphorus in flowering plants at the time of ripe fruits
(calculated excluding any excised tissue).
and deradicated plants but after defoliation (with or without deradication) and
under low nutrient regimes the stem retained high concentrations of
phosphorus. The cauline leaves on defoliated plants (i.e. residual petioles) and
the leaves of plants grown in a heated glasshouse died with high phosphate concentrations present (Table 3).
RESOURCE ALLOCATION IN S M Y R N I U M OLUSATRUM
161
I .o
0.9
0.8
0.7
c
0.6
._
c
e
P
-
c
0.5
f
0
a 0.4
0.3
-C
0.2
P
-
0.1
0
Control
-C
i
Deradicate
Defoliate
Derc
and d
cote
iliate
Low
nutrient
Heated
glasshouse
Figure 3. The effect of treatments upon root: shoot ratios of dry weight (C) and total phosphorus (P)
in flowering plants (calculated excluding weights of excised tissue).
DISCUSSION
The treatments applied to S. olusatmm in these experiments were severe, either
major surgical removal of tissues, severely limiting nutrient supplies or the
continued maintenance of higher temperatures and longer day lengths than
would ever be experienced by the plant in the field. The surgical treatments
mimicked very severe damage by, for example, defoliating insects or the activities
of root pathogens or predators. Nevertheless, very few plants died: two of them
under the low nutrient regime (which much reduced the growth of survivors) and
five that had been both deradicated and defoliated; these died after the onset of
flowering.
Five of the 15 control plants had not flowered at the time of Harvest 2 and the
same proportion of deradicated plants failed to flower. A slightly greater
proportion of plants failed to flower after defoliation (with or without
deradication), low nutrient or heated glasshouse treatments. The variation from
plant to plant in the ability to flower in the second year of growth would not be
surprising if it was clearly effected by treatments, yet the effect of the most severe
treatments, which reduced dry weight at flowering by 80% only slightly reduced
the probability of flowering. It may be that there is genetic variation within
J. LOVETT DOUST
162
Table 3. Mean phosphorus concentrations (mg P/g) (+ S.E.) in selected tissues (at
H2 (second harvest); all data are for plants that flowered and set seed unless
described otherwise)
Dead
basal
leaves
Control
Deradicated
Defoliated
Deradicated
and
Defoliated
H2
reproductive
plants
H2
vegetative
plants
HI
vegetative
plants
H2
reproductive
plants
H2
vegetative
plants
0.96
(0.07)
0.64
(0.02)
1.76
(0.26)
3.07
(0.17)
1.17
(0.07)
2.33
(0.12)
0.99
(0.09)
I .02
(0.06)
I .69
(0.07)
1.75
(0.36)
1.72
(0.19)
3.34
(0.16)
3.29
(0.031
I .03
(0.06)
I .03
(0.05)
0.70
(0.05)
1.87
(0.03)
2.68
10.03)
HI
Low
nutrient
Heated
glasshouse
1.39
0.99
2.0 I
2.34
(0.08)
2.19
(0.23)
4.11
(0.10)
(0.18)
(0.11)
(0.08)
1.51
(0.07)
1.61
(0.09)
4.3 1
(0.17)
2.84
(0.18)
2.17
(0.23)
(0.11)
2.85
(0.13)
2.82
3.25
3.05
(0.18)
(0.11)
(0.10)
1.74
(0.I I )
(0.17)
0.36
(0.03)
2.40
(0.371
4.40
(0.39)
2.87
(0.19)
0.91
(0.031
I .03
(0.06)
4.32
(0.24)
4.07
(0.13)
1.26
(0.06)
3.55
(0.14)
(0.10)
0.40
(0.04)
3.25
(0.31 )
4.46
(0.27)
3.89
(0.16)
2.56
(0.07)
Rays
(tertiary)
2.05
(0.09)
1.35
(0.22)
4.53
(0.35)
7.88
(0.19)
5.49
(0.29)
5.54
(0.3 I )
Fruit
(tertiary)
4.07
(0.21)
3.45
10.13)
(0.15)
4.53
(0.221
4.41
(0.5 1 )
2.83
(0.04)
Tuberous
root
vegetative
plants
Stem
0.71
(0.08)
Dcad
caulinc leaves
Peduncles
I .23
cn.11)
0.93
3.75
3.75
3.62
populations affecting the propensity to flower in the second year of growth.
Variation in the length of the vegetative growth phase in so-called ‘biennials’ has
been observed by other authors e.g., in Daucus carota (Holt, 19721, Dipsacus
fullonum (Werner, 1975a) and Digitalis purpurea (Oxley, in Harper, 1977). Werner
(1975a, b) has shown that in field populations of Dipsacus the probability that an
individual will die, remain vegetative or flower is correlated with the size attained
by the vegetative rosette at the end of the preceding growing season. Flowering
occurs only after the rosette has attained a critical size or weight. No such lower
limit of plant weight appears to be critical for flowering in Smyrnium. The mean
weight of control plants that remained vegetative was considerably greater in the
second year than that of plants that had flowered.
The ability of vegetative plants to continue to grow was reduced by the
removal of half the root system at the end of the first year, but this same
deradication had very little if any effect on the weight achieved by those plants
that did flower. I t was as if, for plants that flowered, half the root system and the
reserves accumulated in it during the first growing season represented luxury
RESOURCE ALLOCATION IN SMYRNIUM OLIISATRUM
1 h3
growth and storage. All other treatments greatly reduced the dry weight of
flowering plants at Harvest 2. The performance of plants under the heated
glasshouse regime was particularly interesting because they maintained a high
rate of leaf production but the rate of leaf death was also high; the effect of the
“favoured” environmental conditions was to increase the flux or turnover of
leaves without increasing the dry weight achieved by the flowering plants.
Very few experimental studies have been made to compare the effects of
defoliation and deradication but two studies are relevant to the interpretation of
the present experiments. Maggs (1964) studied the growth of young apple trees
after (a) removing half the foliage; (b) removing half the root system; and (c)
treatments (a) plus (b). His most striking result was the failure of severe root
pruning to reduce growth. Humphries ( 1 958a, b) examined the growth of barley
after very severe root pruning and he also found no reduction in shoot growth.
In his experiment with the apple Maggs (1964) found that removal of half the
foliage reduced total growth much more than did root pruning. His period of
observation was shorter than in the present study of S . olusatrum. Deradication of
S . olusatrum in addition to defoliation, had only marginally more affect on plant
biomass at Harvest 2 than did defoliation alone.
One may infer some fitness value in the ability of plants to continue life and to
flower and set ripe seed after deradication or continued defoliation. Natural
selection by predators or pathogens may have set the level at which resources are
accumulated and stored well above the minimum required for flowering and
seed set in a hazard-free environment. There is of course no reason to suppose
that evolution optimizes function at the level of the individual. The process of
natural selection is the result of variations in individual fitness, i.e., increase in
the number of descendants that are left by an individual relative to its neighbours.
‘Over-consumption’ or ‘over-production’ may increase an organism’s fitness so
long as this activity deprives neighbours of needed resources.
In these experiments 68 to 74% of plant phosphorus was ultimately found in
reproductive tissues both in control and deradicated plants. There are few
reported studies of phosphorus allocation between plant parts. A study by
Williams (1948) showed that in Awena satiwa (an annual) growing at low and
medium phosphorus levels, 72 to 78% of accumulated phosphorus was eventually
allocated to the inflorescence. In the annual Senecio syluaticus, Van Andel 8c Vera
(1977) found that 35 to 57% of accumulated phosphorus was ultimately allocated
to reproductive organs by plants grown at the low and medium nutrient levels.
They found that the growth of the perennial, Chamaenerion angustfolium was less
responsive to nutrient level than S. syluaticus and the allocation of phosphorus to
reproductive activities in C. angustfolium was only 15 to 18%. In a study of
phosphate allocation in the banana (a perennial) which did not take allocation to
roots into account, Twyford 8c Walmsley (1974) found 26% of plant phosphorus
was allocated to reproductive organs. The proportion of phosphorus allocated to
reproductive organs in the biennial S. olusatrum was therefore considerably
higher than that reported for perennials and closer to the values reported in
annuals. It was not surprising that higher proportions of plant phosphorus than
of total biomass are allocated to reproduction bearing in mind that a large
fraction of biomass is represented by non- translocatable
structural
carbohydrate, whereas phosphorus is one of the elements that remains relatively
mobile within plant tissues.
164
J . LOVETT DOUST
Only control plants and deradicated plants contained significantly more
phosphorus at the fruiting stage than they did at Harvest 1. It is therefore
presumed that the defoliated plants (with or without deradication), those grown
at low nutrients and those grown in the heated glasshouse, rovided all or most
of the phsophorus for their reproductive organs by redistri
! k ution of phosphate
already taken up in the first ten months of growth.
Figures 1 and 2 illustrate by menas of pie diagrams the proportionate allocation
of biomass and of phosphorus among the organs of flowering plants at
maturity. Deradication slightly increased the proportion of phosphorus allocated
to reproductive structures but defoliation reduced, and deradication with
defoliation, the low nutrient treatment and the heated glasshouse treatment, all
greatly reduced the proportion of total phosphorus allocated to reproductive
structures. In the two defoliated regimes and in the low nutrient regime a very
much greater proportion of the phosphorus was retained in the tuberous root
system; and under heated glasshouse conditions a large fraction of plant
phosphorus was lost in the dead leaves that were accumulated as a result of the
very high birth and death rates of leaves on plants growing in this regime.
The amounts of phosphorus present in different plant organs reflect in part
the different allocations of biomass (dry weight) to the different categories of
organ. Measures of the concentration of phosphorus within various organs give a
different picture, perhaps more indicative of the extent to which particular
structures may be depleted of phosphorus during the process of reallocation at
fruit formation. The concentrations of phosphorus in fruits (Table 3) varied only
slightly between treatments (between 3.5 and 4.5 mg P/g dry weight) except that
under heated glasshouse conditions fruits of low phosphate content were
formed. In the control and deradicated plants phosphorus concentrations fell to
very low levels in the stem, rays and peduncles but in plants receiving the other
treatments, all of which greatly reduced total growth, the concentrations of
phosphorus in these organs remained high. This suggests that internal
phosphorus concentrations were perhaps limiting during fruit formation in those
plants that had grown large and that consequently, during fruit ripening, more
completely drained the rays and peduncles of phosphate content than was the
case in plants that had made less growth and in which internal phosphate levels
might not have been limiting. Phosphate concentration in the tuberous root also
declined sharply in control and deradicated plants that flowered, again
suggesting that it was in the plants that had grown most vigorously that the
vegetative organs were most depleted of phosphate when it was required for
ripening of the large amount of fruit formed under these conditions. In marked
contrast, the phosphate concentration in the root system did not fall
significant?, and in some cases actually increased, in plants that were grown
under con itions that greatly reduced plant biomass.
Lovett Doust & Harper ( 1980) reported the pattern of resource allocation
to stamens, pistils, petals and stylopodia in these plants and showed it to be very
fixed in nature. Stebbins (1950) has argued that characters formed by long
periods of meristematic activity (for instance total plant size, o r leaf number) will
be more subject to environmental influences and are likely to be more plastic
than characters formed relatively rapidly (such as floral organs). Clear plasticities
in reproductive allocation are known to exist, e.g. in iteroparous plants there
may be whole years in which vegetative growth occurs and no flowers are
RESOURCE ALLOCATION IN SMYRNIUM OLUSATRUM
165
produced, and Hickman (1975; 1977) has shown that there is some plasticity in
the allocation of biomass to reproductive organs in species of Polygonum. The
present study indicates that the homeostatic processes in S. olusatrum maintain
patterns ofallocation in whole plants only within wide limits ofvariation.
Reproduction is a lethal activity in Smyrnium olusatrum. At the time ot fruit
formation biomass becomes concentrated in the fruits, and phosphorus more
strikingly so. I t is as if demands made on limited resources by the process of fruit
filling deplete the plant of resources that might otherwise be used in continued
vegetative growth and perennation. Only in those flowering plants that were
inhibited in growth by defoliation, mineral deficiency, or the high leaf death rate
in the heated glasshouse were relatively high phosphate levels maintained in
vegetative structures at the time of flowering. I t might be suggested that internal
phosphorus resources were adequate to supply the limited number of fruits
formed under these conditions without drawing on the reserves in other tissues.
In general those plants that failed to flower and persisted in a vegetative
condition also maintained high phosphate concentrations in the vegetative
organs. The pattern of resource allocation in S. olusatrum a 'biennial'
semelparous species with lethal reproduction, is very similar to that described for
the oat (Williams, 1948). The contrast with the perennial iteroparous
Chamaenerion angustfolium is striking (Van Andel 8c Vera, 1977). In Chamaenerion a
low proportion of phosphorus was allocated to fruits and phosphate concentrations remained high in other tissues. Sufficient resources were left within
the plant after flowering to permit renewed vegetative growth and activity in
subsequent years. This suggests that the death of monocarpic plants after seed set
may be a direct consequence of the depletion of resource levels in the vegetative
tissues below that necessary to sustain future meristematic growth.
ACKNOWLEDGEMENTS
I am grateful to ProfessorJ. L. Harper and Drs L. M. Lovett Doust, P. B. Cavers
and M. A. Maun for their helpful suggestions and comments.
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