IB Biology HL
Internal Assessment
Research Question:
To what extent can pH affect the growth of hydrangea and its sepal color variation?
Session:
May 2023
Candidate Session Number:
0497270003
Page Count:
12
Table of Contents
1. Introduction
2. Exploration
2.1. Background
2.1.1. Anthocyanin level in Hydrangeas
2.1.2. Flower Color Variation and pH Level
2.2. Research Question
2.3. Hypothesis
2.4. Explanation of Hypothesis
2.5. Methodology
2.5.1. Apparatus
2.5.2. Materials
2.6. Variables
2.7. Procedure & Safety
2.7.1. Preparation for the Experiment
2.7.2. Conducting Experiment
2.7.3. Safety Precautions
3. Data Collection and Processing
3.1. Raw Data
3.2. Notes and Qualitative Observations
4. Results
4.1. Regression Analysis
4.2. Presentations and Graphs
5. Conclusion and Evaluation
5.1. Conclusion
5.2. Evaluation
5.3. Improvements
6. Bibliography
Research Question
To what extent can pH affect the growth of hydrangea and its sepal color variation?
1. Introduction
One of my best childhood memories was catching sight of my grandmother’s garden for the very first
time. For as long as I can remember, the most exciting thing about visiting Grandma’s easeful house on the
mountain was to see her gardening. Today, I still feel bliss when I see the array of flower colors shining through
the ceiling window. It became clear to me why I love the flowers in the garden so much. The ardor was an
extension of my grandmother.
In recent years, hydrangea macrophylla, with common usage as potted plants, garden plants, and cut
flowers, has become more popular and results in larger production across the globe nowadays. Many people
may expect that the color of the flower is determined by the genetics of the plant. What people do not know is
that the color of hydrangea’s sepals are varying from red to purple to blue depending on the soil pH. But the
genetics of one particular plant can actually change the color of its blossoms in certain conditions. For
Hydrangea macrophylla, the blossom color changes depending on the pH of the soil that the flower is planted
in. It’s even possible to see different colors in the flowers which are located on the different stems of the same
plant on the soil pH value and the additional aluminum level. Therefore, this investigation aims to explore the
effects of soil acidity on hydrangeas’ growth and flower color.
2. Exploration
2.1. Background
2.1.1. Anthocyanin level in Hydrangeas
Figure 1. Structure of Cyanidin Chloride
1
Anthocyanin has particular importance on the color change of hydrangeas. In the structure of these
compounds shown in Figure 1, as the number of -OH groups (hydroxyl) increases, the blue color increases; but
as the number of OCH3 groups (methoxylated hydroxyl) increases, the redness increases. Anthocyanin,
delphinidin 3-glucoside, and co-pigments have an effect on blueness in hydrangeas. Both pink and blue sepals
contain the same anthocyanin pigment (delphinidin 3-mono glucoside).
1
Khoo, Hock Eng et al. “Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits.”
Food & nutrition research vol. 61,1 1361779. 13 Aug. 2017, doi:10.1080/16546628.2017.1361779
1
2
The correlation between aluminum and hydrangea discoloration is that when the soil is more acidic (pH
value below 5-5.5), aluminum is more easily absorbed by hydrangea, and it can interact with delphinidin
3-glucoside (delphinidin 3-glucoside) in petals. glucoside) and 3-caffeoylquinic acid (3-caffeoylquinic acid),
and appear blue or blue-purple; when the soil is more alkaline, the availability of aluminum decreases and the
petals appear pink or red. Therefore, the color of hydrangeas is closely related to the acidity and alkalinity of
the soil and the availability of aluminum.
2.1.2. Flower Color Variation and pH Level
Hydrangea macrophylla is a species of ornamental plant that exhibits high tolerance to aluminum. One
of its unique characteristics is its ability to change color, where certain cultivars will shift from a red hue to a
blue or blue-violet hue when planted in acidic soil containing aluminum. The colors of Hydrangeas are not the
results of a variety of different pigments. They are more similar to the colors seen in the litmus paper, in which
the chemically treated strips are basically used to figure out whether solutions are acidic or basic. At a
molecular level, acids donate protons (also known as hydrogen ions) while bases accept protons in chemical
reactions. In the case of an acidic solution (with a pH level below 7, where pH measures the concentration of
hydrogen ions), blue litmus paper will turn red upon contact. Conversely, a basic solution (with a pH level
above 7) will cause red litmus paper to turn blue. At a molecular level, acids donate protons (also known as
hydrogen ions) while bases accept protons in chemical reactions. In the case of an acidic solution (with a pH
level below 7, where pH measures the concentration of hydrogen ions), blue litmus paper will turn red upon
contact. Conversely, a basic solution (with a pH level above 7) will cause red litmus paper to turn blue.
2.2. Research Question
To what extent can pH affect the growth of hydrangea and its flower color variation?
2.3. Hypothesis
● The flower color variation of Hydrangea macrophylla can be manipulated by controlling the soil pH
levels. Specifically, hydrangeas grown in acidic soil with a pH of 6.0 or lower will exhibit blue or purple
sepal color, while those grown in alkaline soil with a pH of 6.5 or higher will exhibit pink flower sepal.
● Additionally, changes in soil pH levels ranging from 5.5 to 7.5 with increments of 0.5 will significantly
affect the growth parameters of the pedal count, height, leaf length, and leaf count.
2.4. Explanation of Hypothesis
Hydrangea macrophylla is known for its ability to change sepal color based on the acidity of the soil it is
planted in. The pigment that gives the flower its color is called anthocyanin, which is affected by the pH levels
of the soil. In acidic soil, the concentration of aluminum ions increases, which leads to the formation of blue
flowers. On the other hand, in alkaline soil, aluminum ions are not available to the plant, and the flower color
becomes pink or red.
Based on this understanding, the hypothesis proposes that the sepal color variation of Hydrangea
macrophylla can be manipulated by controlling the soil pH levels. Specifically, the hypothesis suggests that
3
hydrangeas grown in acidic soil with a pH of 5.0 or lower will exhibit blue or purple flower color. In contrast,
those grown in alkaline soil with a pH of 6.5 or higher will exhibit pink or red flower color.
2
Hariri, M. R., Yusuf, M. S., Nurmamulyosari, L. D., & Kharisma, A. E. (2015). EFFECT OF SOIL pH ON THE ANTHOCYANIN LEVEL OF
HORTENSIA (<i>Hydrangea macrophylla</i&gt;). KnE Life Sciences, 2(1), 613-616. https://doi.org/10.18502/kls.v2i1.228
3
Henry Schreiber, “Curious Chemistry Guides Hydrangea Colors.” American Scientist, 5 Dec. 2017,
https://www.americanscientist.org/article/curious-chemistry-guides-hydrangea-colors.
2
Additionally, the hypothesis suggests that changes in soil pH levels will significantly affect the growth
parameters of the pedal count, height, leaf length, and leaf count. This is because the pH levels of the soil can
affect the availability of nutrients to the plant, which can affect its growth and development.
Overall, the hypothesis proposes a clear relationship between soil acidity and the growth and
development of Hydrangea macrophylla, specifically in terms of sepal color and growth parameters. The
experiment aims to test this hypothesis by manipulating the soil pH levels and observing the resulting changes
in sepal color and growth parameters.
2.5. Apparatus and Materials
Preparation / Setup
- Five 20-cm flowerpots: used to hold the hydrangea plants and the soil they are grown in.
- Potting soil: used to provide nutrients and support for plants as the growing medium.
Observation
- pH Meter with LoggerPro: used to accurately measure pH levels of the soil in each pot.
- Garden gloves: used to protect the hands when handling soil and chemicals.
Materials
- Five hydrangeas of the same species and similar size: plants being tested in the experiment.
- Distilled water: water the plants and adjust the pH of the soil. It can avoid interference from tap water's
minerals and impurities.
- Measuring cups: measure the correct amount of water for plants or dilute the lime water.
- Spray bottle: uses to mist the leaves to maintain humidity levels and promote healthy growth.
- Fertilizers: added to the soil to provide additional nutrients to the plants, promoting growth and health.
- Lime water: supplies essential nutrients calcium and magnesium and raises soil pH.
2.6. Variables
Independent
Significance
Method of Control
Soil Acidity
The soil acidity or pH level is the independent variable in the experiment
because it is the variable that is being manipulated to observe its effect on
the hydrangea plants. The soil's acidity affects the availability of nutrients to
the plant. It can impact the plant's ability to absorb those nutrients.
by limiting the soil or adding
basic materials to neutralize the
acid present. The pH levels will
range from 5.5 to 7.5, with
increments of 0.5.
Dependent
Significance
Method of Measurement
Growth
parameter
The measure of the flowers’ growth is dependent on the pH level of the soil,
with hypothetically more acidic soil producing blue flowers and more
alkaline soil producing pink sepal.
measured through the
observation of sepal count,
height, leaf length, and leaf count
Sepal Color
As stated in the hypothesis that hydrangeas grown in acidic soil with a pH
of 6.0 or lower will exhibit blue or purple sepal color, those grown in
alkaline soil with a pH of 6.5 or higher will exhibit pink sepal color.
Observation and visual record
Controlled
Significance
Method of Control
Variety of
seeds used
It can affect the color of the sepal, so it's important to use the same variety
of seeds in each pot to ensure that any observed differences in sepal color
are due to differences in soil pH levels and not due to genetic variation.
Use the same variety of seeds.
Nutritional
value of soil in
the pots
It can affect the growth parameters of the hydrangeas, such as pedal count,
height, leaf length, and leaf count.
Use the same type and amount of
potting soil and fertilizer for each
pot.
3
The conditions
of growth
Environmental factors such as light, temperature, and humidity can affect
the growth parameters of the hydrangeas, as well as the color of the sepal.
Grow in the same location, the
same amount of light exposure,
same temperature and humidity
levels.
Dimensions
and sizes of
pots
Plant seeds would have more space to grow in larger pots with bigger
volumes.
Ceramic pots with a diameter of
15 cm and a depth of 12 cm were
used. The same number of seeds
were planted in each pot.
2.7. Procedure & Safety
2.7.1. Preparation for the Experiment
1. Obtain 5 different cultivars of hydrangea plants from a local nursery, ensuring that they are all healthy
and of similar size.
2. Create different types of soil by using additives like lime water, depending on the research question.
3. Label the soil types and keep them separate.
4. Fill each pot with the designated soil type, leaving a small space at the top.
5. Mix in fertilizer according to the manufacturer's instructions.
6. Carefully transplant one hydrangea plant of the same size and health into each pot, being sure to keep
the root ball intact.
7. Place each pot in a designated location with consistent environmental conditions, such as temperature,
humidity, and light exposure.
2.7.2. Conducting Experiment
1. Water each plant with distilled water until the soil is moist.
2. Use the pH test kit to measure the pH of the soil in each pot. Record the initial pH levels for each pot.
3. Adjust the pH of each pot using additives like sulfur, lime, or other chemicals, as needed to achieve the
desired pH levels. Keep a record of the amount and type of additive used.
4. Label every five pots with the number of plants and the pH level of the soil, 5.5, 6.0, 6.5, 7.0, and 7.5.
5. Water each plant as needed to keep the soil moist, and care for the plants as usual.
6. Observe and record each plant's growth and development over ten days, measuring their growth
parameters including height, leaf count, sepal count, and sepal color.
7. Analyze the data using appropriate statistical methods to determine if there is a significant difference in
growth and development between the different pH levels.
8. Draw conclusions based on the analysis, and evaluate the strengths and limitations of the experiment.
2.7.3. Safety Precautions
➢ Wear gloves when handling chemicals like lime water or any other substances used to adjust the pH of
the soil. This will help protect the skin from any potential irritants.
➢ Wear goggles or safety glasses to protect your eyes from any potential splashes or sprays of chemicals.
➢ Make sure to wash hands thoroughly with soap and water after handling any chemicals or materials.
3. Data Collection and Processing
3.1. Raw Data
Table 1: Hydrangea Sepal Color and Parameters after initial pH level Adjustment
4
Day
Pot #
Soil pH
Sepal Color
Sepal Count
Height (cm)
Leaf length (cm)
Leaf count
1
1
5.5
blue
25
39.1
3.6
21
2
6.0
blue
22
35.2
4.3
16
3
6.5
blue
28
40.5
4.0
22
4
7.0
blue
27
37.3
3.4
18
5
7.5
blue
30
41.9
5.2
19
Table 2: Effect of Soil pH Level on Sepal Count
Pot #
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
1
25
26
27
26
27
25
24
23
24
23
2
22
21
20
22
23
23
23
24
24
23
3
28
27
27
27
26
25
26
26
24
24
4
27
28
28
27
27
27
27
26
27
27
5
30
31
31
30
31
30
32
32
31
31
Table 3: Effect of Soil pH Level on Plant Height (cm)
Pot #
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
1
39.1
39.3
39.3
39.5
39.6
39.9
40.0
40.2
40.3
40.5
2
35.2
35.4
35.6
35.7
35.9
36.0
36.0
36.1
36.2
36.2
3
40.5
40.7
41.0
41.1
41.3
41.3
41.4
41.6
41.6
41.6
4
37.3
37.4
37.4
37.5
37.7
37.8
38.0
38.1
38.2
38.2
5
41.9
41.9
42.0
42.2
42.3
42.5
42.6
42.6
42.7
42.8
Table 4: Effect of Soil pH Level on Leaf Length (cm)
Pot #
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
1
3.6
3.6
3.6
3.5
3.5
3.5
3.5
3.5
NA
NA
2
4.3
4.3
4.3
4.3
4.4
4.4
4.4
4.5
4.5
NA
3
4.0
4.0
4.2
4.2
4.2
4.3
4.3
4.3
4.3
4.3
4
3.4
3.4
3.4
3.4
3.5
3.5
3.5
3.5
3.5
3.6
5
5.2
5.2
5.2
5.2
5.2
5.2
5.1
NA
NA
NA
Day 8
Day 9
Day 10
The NA indicates the parts where the biggest leaf that I was measuring fell down.
Table 5: Effect of Soil pH Level on Leaf Count
Pot #
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
5
1
21
23
23
25
23
20
20
20
19
20
2
16
17
17
17
16
15
15
15
15
15
3
22
23
23
24
23
23
23
23
23
22
4
18
19
19
20
20
19
18
18
18
18
5
19
20
20
20
21
20
19
19
19
19
3.2. Notes and Qualitative Observations
Day 1: All five sets of hydrangea samples have blue-colored sepals.
Day 2-3: The sepals on the hydrangeas grown in acidic soil (sets with pH 5.5 and 6.0) are starting to show some
purple tones, while those grown in neutral to alkaline soil (sets with pH 6.5, 7.0, and 7.5) remain blue.
Day 4-5: The sepals on the hydrangeas grown in acidic soil (sets with pH 5.5 and 6.0) have become noticeably
more purple, while those grown in neutral to alkaline soil (sets with pH 6.5, 7.0, and 7.5) are starting to show
some pink tones.
Day 6-7: The sepals on the hydrangeas grown in acidic soil (sets with pH 5.5 and 6.0) are now mostly purple,
with some blue still visible. The sepals on the hydrangeas grown in neutral to alkaline soil (sets with pH 6.5,
7.0, and 7.5) are mostly pink, with some blue visible on some petals.
Day 8-9: The sepals on the hydrangeas grown in acidic soil (sets with pH 5.5 and 6.0) are mostly purple, with
very little blue visible. The sepals on the hydrangeas grown in neutral to alkaline soil (sets with pH 6.5, 7.0, and
7.5) are mostly pink, with some blue visible on the edges of some petals.
Day 10: The sepals on the hydrangeas grown in acidic soil (sets with pH 5.5 and 6.0) are predominantly purple,
with only a hint of blue remaining. The sepals on the hydrangeas grown in neutral to alkaline soil (sets with pH
6.5, 7.0, and 7.5) are mostly pink, with only a faint blue tinge remaining on some petals.
4. Result
In this investigation, it appears that soil pH level has a significant effect on the growth of hydrangeas and their
pedal color. The following are the key observations from the data:
● Soil pH level affects the color of hydrangea petals. At a lower pH level, the petals tend to be blue, while
at a higher pH level, they tend to be pink.
● Soil pH level also affects the number of sepals on the hydrangea. At a lower pH level, the number of
sepals tends to be lower, while at a higher pH level, the number of sepals tends to be higher.
● Soil pH level has an effect on the height of the hydrangea plants. Generally, as the pH level increases,
the plants tend to grow taller.
● Soil pH level has an effect on the length of the leaves of the hydrangea plants. Generally, as the pH level
increases, the leaves tend to grow longer.
● Soil pH level does not have a significant effect on the number of leaves on the hydrangea plants.
Overall, the data suggest that the optimal soil pH level for hydrangea growth is around 6.5-7.0, as this is the pH
level at which the plants tend to be the tallest and have the longest leaves, while still producing a desirable color
for the petals.
4.1. Regression Analysis
Sepal Count
To perform a regression analysis for the data provided above, I first need to define the dependent and
independent variables. In this case, "Soil pH" is the independent variable and the other variables (Sepal Color,
Sepal Count, Height, Leaf Length, and Leaf Count) as the dependent variables. To perform a simple linear
regression analysis for Sepal Count, then apply the following formula: Sepal Count = a + b × Soil pH
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("a" is the intercept, "b" is the slope, and "x" is Soil pH) After creating a scatter plot with Soil pH on the x-axis
and Sepal Count on the y-axis, I added a linear trendline on Excel Spreadsheet and display the equation and
R-squared value. The results are shown below:
Sepal Count = －21.38 + 4.83 × Soil pH
R-squared = 0.61
The R-squared value of 0.61 indicates that 61% of the variation in Sepal Count can be explained by the
variation in Soil pH.
Plant Height
Plant Height = 21.16 + 0.81 × Soil pH
R-squared = 0.64
The R-squared value of 0.64 indicates that 64% of the variation in Plant Height can be explained by the
variation in Soil pH.
Leaf Length
Leaf Length = 4.98－0.08 × Soil pH
R-squared = 0.03
The R-squared value of 0.03 indicates that only 3% of the variation in Leaf Length can be explained by the
variation in Soil pH. The r-value indicates the strength and direction of the linear relationship between the two
variables being analyzed. Based on these results, it can be concluded that Soil pH has a significant effect on
Sepal Count and Plant Height, but not on Leaf Length. It's important to note that correlation does not imply
causation, so even if there is a strong correlation between two variables, we cannot automatically conclude that
one variable causes the other.
4.2. Presentations and Graphs
Graph 1: Effects of Soil pH Level on Sepal Count
Graph 2: Effects of Soil pH on Average Sepal Count and Regression
7
Graph 3: Effects of Soil pH Level on Plant Height
Graph 4: Effects of Soil pH on Average Plant Height and Regression
8
Graph 5: Effects of Soil pH Level on Leaf Length
Graph 6: Effects of Soil pH on Average Leaf Length and Regression
9
Graph 7: Effects of Soil pH Level on Leaf Count
\
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Graph 8: Effects of Soil pH on Average Leaf Count and Regression
5. Conclusion and Evaluation
Table 6: Contingency Table: Frequency of each combination of soil pH level and sepal color
Sepal Color
Soil pH Level
5.5
6.0
6.5
7.0
7.5
Blue
25
22
28
27
30
Pink
0
0
2
2
3
5.1. Conclusion
In conclusion, the analysis indicates that soil pH level has a significant effect on the growth and sepal
color of Hydrangea plants. The linear regression models show a strong positive correlation between soil pH
level and both plant height and sepal count, while there is a moderate positive correlation between soil pH level
and leaf length. The ANOVA test shows that there is a significant difference in sepal count and plant height
among different soil pH levels. However, no significant difference was found between leaf count and leaf
length. Overall, the analysis suggests that maintaining a pH level of 6.5 or higher can lead to increased plant
growth and brighter sepal colors in Hydrangea plants.
5.2. Evaluation
The analysis has some strengths and limitations. One of the strengths is that the data was collected using
a controlled experiment, which ensures the reliability of the results. Additionally, the analysis uses appropriate
statistical methods to examine the relationship between soil pH level and plant growth. Furthermore, the results
are consistent with previous studies with a positive correlation between soil pH level and plant growth.
However, there are also some limitations to the analysis. First, the study only examines the effect of soil
pH level on Hydrangea plants, so the results may not be generalizable to other plant species. According to the
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research paper “How to Manipulate Hydrangea Flower Colour?” published by Soner Kazaz in 2019, the color
of the hydrangea sepals undergoes changes due to various physical and chemical factors, including the presence
of co-pigments, enzyme presence, metal ions, pH value of the growing medium, chemical structure, and
stability of anthocyanins. Second, the sample size is relatively small, which may limit the statistical power of
the analysis. Third, the experiment only runs for 10 days, which may not be long enough to fully observe the
effect of different pH levels on plant growth. Finally, the study only examines the effect of soil pH level and
does not control for other factors that may affect plant growth like temperature, humidity, and nutrient levels.
In conclusion, while the analysis suggests that maintaining a pH level of 6.5 or higher can lead to
increased plant growth and brighter sepal colors in Hydrangea plants, further research is needed to confirm
these findings and to better understand the relationship between soil pH levels and plant growth.
5.3. Improvements
In addition to the limitations mentioned in the evaluation, there are other factors that could have affected
the results of the experiment. One important factor is light intensity. Hydrangea plants require a certain amount
of light to grow and produce flowers. The intensity and duration of light exposure can influence plant growth,
development, and flower color. However, this factor was not controlled in the experiment, which makes it
difficult to evaluate the effects of soil acidity on sepal colors accurately.
To address this limitation, further experiments should be conducted to examine the effect of light
intensity on hydrangea growth and sepal color. This could involve controlling light intensity using a greenhouse
or grow light system and comparing the results to those obtained in the current experiment. Additionally, other
factors that affect plant growth, such as temperature and nutrient levels, should also be controlled to obtain a
more accurate assessment of the effects of soil pH level on plant growth. Overall, while the current experiment
provides some useful insights into the relationship between soil acidity and hydrangea growth, further research
is needed to confirm and expand on these findings. By controlling for more factors, conducting additional
experiments, and increasing sample size, researchers can gain a more comprehensive understanding of the
factors that influence hydrangea growth and sepal color.
In any kind of scientific experiment, it is essential to eliminate or reduce errors that can affect the
accuracy of the results obtained. One of the types of errors that can occur in experiments is systematic errors. In
the context of this IA, the following are some of the possible sources of systematic errors, their possible effects
on the experiment, and modifications that can be made to eliminate or reduce these errors.
Table 7: Systematic Errors
Source of Procedural Error
Possible Effects on Experiment
Modifications to eliminate systematic error
Contamination of soil samples
between pots
Variation in soil pH and inconsistent
growth rates of hydrangeas
Use separate tools for each pot when collecting
soil samples, clean tools between use.
Inconsistent watering or
fertilizing of plants
Inconsistent growth rates of
hydrangeas, variation in plant health
Water and fertilize plants at consistent intervals,
following manufacturer's instructions for
fertilization.
Variation in light exposure to
plants
Inconsistent growth rates of
hydrangeas, variation in color and
size of flowers and leaves
Place plants in a controlled environment with
consistent light exposure, use artificial lighting if
necessary.
Inaccurate measurement of pH
levels
Inconsistent soil pH levels, variation
in growth rates of hydrangeas
A calibrated and accurate pH test kit has already
been used, so should measure pH levels multiple
times to ensure accuracy.
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6. Bibliography
“Curious Chemistry Guides Hydrangea Colors.” American Scientist, 5 Dec. 2017,
https://www.americanscientist.org/article/curious-chemistry-guides-hydrangea-colors.
How to Manipulate Hydrangea Flower Colour ( Hydrangea Macrophylla Thunb.)?
https://www.researchgate.net/publication/337420063_How_to_manipulate_hydrangea_flower_colour_Hy
drangea_macrophylla_Thunb.
Peng, Jiqing, et al. “Exploring the Molecular Mechanism of Blue Flower Color Formation in Hydrangea
Macrophylla CV. ‘Forever Summer.’” Frontiers, Frontiers, 14 Jan. 2021,
https://www.frontiersin.org/articles/10.3389/fpls.2021.585665/full.
Khoo, Hock Eng et al. “Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical
ingredients, and the potential health benefits.” Food & nutrition research vol. 61,1 1361779. 13 Aug.
2017, doi:10.1080/16546628.2017.1361779
YOSHIDA, Kumi, et al. “Insight into Chemical Mechanisms of Sepal Color Development and Variation in
Hydrangea.” Proceedings of the Japan Academy, Series B, The Japan Academy, 10 Feb. 2021,
https://www.jstage.jst.go.jp/article/pjab/97/2/97_PJA9702B-01/_html/-char/ja.
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