THE EFFECT OF LIGHT INTENSITY
ON THE PHOTOSYNTHETEC
EFFICEENCY OF CARNATEON

VAREETEES

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THE EFFECT OF LIGHT INTENSITY
ON THE PHOTOSYNTHETIC EFFICIENCY
OF CARNATION VARIETIES

By
WINFRED DAVIS HOLLEY

A THESIS
Submitted to the Graduate School of Michigan
State College of Agriculture and Applied
Science in partial fulfilment of the
requirements for the degree of

MASTER OF SCIENCE

Department of Horticulture

1940

CégéakA4fiVi?/‘/Q4Lfi7'2;::£::;f29

THESIS

 

TABLE OF CONTENTS

Page
Introduction ---------- 1
Review of Literature ------ 2
General Procedure - ------ 5
Experimental Results ------ 9
Discussion ----------- 24
Summary ------------ 26
Literature Cited -------- 27
Adknowledgements -------- 29

Introduction

The greenhouse carnation is one of the most widely grown
of florists' crops. Although methods of culture have been ra-
ther generally agreed upon, many carnations of poor quality are
found on the markets during the winter months. Flowers producai
in sections where cloudy weather prevails are noticeably weaker
of stem than those produced under more favorable light condi-
tions.

It has been a common practice to grow all varieties of car-
nations under whatever conditions may prevail. Possibly-these
conditions are most favorable only for the most prolific varie-
ties. Certain varieties consistently produce more flowers per
season, including a higher production during the cloudy months
from December to February. Production is undoubtably tied up
with heredity, but it may be directly due to photosynthetic ef-
ficiency. Are these more prolific varieties capable of utiliz-
ing lower light intensities more efficiently? Presumably, the
accumulation of the products of photosynthesis over and above
those used in respiration determines largely the production.
How do different varieties respond to different intensities of
light? Experiments were designed and carried out to secure re-

sults that might serve in giving an answer to that question.

Review of Literature

Light is only one of the many factors that influence the
rate of photosynthesis in green plants. Blackman and Matthaei
(2), under properly controlled conditions, concluded that if the
temperature and carbon dioxide are in excess, the rate of photo-
synthesis is prOportional to the intensity of incident light.
For every temperature there is a maximum light intensity which
will produce a maximum rate of photosynthesis at that temperature.

Combes (3) grew potatoes and other tuber-forming species
under different light intensities. He concluded that the higher
the light intensity, the greater the accumulation of elaborated
organic compounds in the storage parts of the plants. Apparent-
ly, at lower intensities the storage function ceased and the en-
tire amount of the products of photosynthesis was consumed in
the growth of parts of the plants other than storage organs.
Combes also found, for a majority of species studied, that Opti-
mum light intensity varied with the growth stage of the plant.
Higher light intensities were required during the period from
flowering to maturity than were necessary for optimum dry weight
increase in the earlier stages of growth.

Tincker (13) made similar conclusions, working with Dahlia
and several other tuberous rooted and root-storing species. He
obtained taller plants by supplementing 12 hours of daylight
with weak electric lights, but there was very littIe storage
under such conditions. Plants receiving only 12 hours of day-
light were shorter but had good storage root systems. Appar-

ently the weak electric-lights stimulated top growth at the ex-

panes of the storage function. Tincker also found that the

average storage under 5 to 6 hours of daylight was only 17 per-
cent of that under 10 to 12 hours of daylight. The shorter per-
iOd of light produced only enough food materials for top growth.

Working with the garden pea, De Besteriro and Durand (6)
found a dry-weight increase in direct proportion to the intensity
employed for its irradiation.

Porter (10), working with greenhouse tomatoes under dif-
ferent light intensities, found the percentages of dry matter,
ash material, fresh weight and elaborated food materials to cor-
relate rather closely with the light intensity received by the
plants. He concluded that light intensity variation is the
chief cause of differences in plant efficiency.

Popp (9) grew four varieties of soybeans for 7 days at a
temperature of 19 to 23°C. under light intensities of 4,285,
1,538, 560, 590, 250, and 26 foot-candles, respectively. He
observed that the lower the light intensity the more rapid was
the rate of stem elongation during the period of initial growth.
The greatest general height was attained by plants under a light
intensity averaging 560 foot-candles and the lowest under 26
foot-candles. The thickness of the stem was directly prepor-
tional to the light intensity, and there was a gradual decrease in
vigor with decreasing light intensity.

Dastur and Samant (5), working under artificial and natural
light conditions, reported that the production of starch, total
carbohydrates, and total sugars is much greater in diffuse day-
light than in artificial light. They attributed these differ-

ences not to any variations in intensity but to a difference in

 

 

the quality of the light. Dastur and Mehta (4) concluded that
in using artificial light, photosynthetic activity is highest
in white light, intermediate in red light and very feeble in
the blue-violet region of the spectrum.

The foregoing are only a few of the numerous investigators
' who have worked with light and its relation to plant growth.
Artificial light has been used in many instances as a method of
forcing greenhouse plants. Tjebbes (14) and Hostermann (8)
obtained earlier and larger yields of various greenhouse creps
by supplementing winter daylight with eight hours of electric
light.

Literature on the use of light on carnations is not plen-
tiful. Arthur et. a1. (1) grew various greenhouse plants un-
der artificial climatic conditions. Additional light and car-
bon dioiide gave no reaponse with carnations; however, some or-
namentals, such as roses, sweet peas, snapdragons, petunias and
nasturtiums, grew and flowered remarkably well. Their results
with carnations may have been due to the comparatively high
temperature used (78°F), since carnations grow best at cooler
temperatures.

Ramaley (12), working with carnations, and other caryOphyl-
laceous plants, found that continuous illumination caused car-
nations to bloom appreciably earlier than check plants. There
was no difference in appearance between treated and untreated
plants. Light intensities of 10-20 foot-cardles were used dur-
ing the night. Withrow and Richman (15) grew the Pink Abundance

variety of carnation, using 16 foot—candles of light for 10

hours as a supplement to winter daylight. The additional

light increased both flower production and length of stem,

but the variety produced fewer new shoots than control plants.
Recent work on the carnation at Cornell University (11) yield-
ed similar results. Low intensity lights were not beneficial
when used 6 hours or less. High intensity lights hastened pro—
.duction considerably but at cost too great to be profitable.
This work and the work by Withrow and Richman (15) indicate that
supplementing daylight with artificial light is not a profitable
method of increasing carnation production, since high intensit-
ies of light are necessary. Perhaps it would be possible to sel-
ect certain varieties that are more efficient in using lower in-
tensities of light. A comparison of the leaf efficiency of sev-

eral varieties should furnish needed information.
General Procedure

The three varieties of carnations used in this experiment
were: Morning Glow, a good producer from the standpoint of num-
ber of blooms; Maine Sunshine, an average producer; and Pelargon-
ium, a poor producer under local conditions.

It was first necessary to determine as accurately as pos-
sible the relative growth rates for the three varieties under

plants of each

natural daylight corditiors. On Fay 31, 150
variety were selected and potted in 5 inch pots. These plants
had been propagated by cuttings the previous winter and had

been grown under identical conditions for one month previous

to potting.

The soil used in potting consisted of 2 parts of heavy
loam compost, 1 part leaf mold and a small amount of sand.
Super-phosphate was added at the rate of one 3 inch potful
to 2 bushels of soil. The soil was mixed by thorough shovel-
1ing-over and was as uniform as could be obtained.

Water was applied sparingly for the first month, since
the plants were over-potted at the outset to avoid shifting
at anytime during the eXperiment. The leaf area on all plants
was made as uniform as possible by pinching some plants and
partial defoliation of others. ~The plants were placed on moist
sand, in a sunny house on June 1. The varieties were arranged
in alternating rows as follows: a row of 10 of the Morning
Glow variety, then a row of 10 of Pelargonium, followed by 10
of the variety “aine Sunshine, after which the sequence was
repeated.

On June 15, 35 whole plants of each variety were taken;
washed; dried to constant weight in an oven at 70°C., then
weighed individually. In taking them from the bench, every
fourth plant of each variety was taken. Dry weights of 35
plants of each variety were obtained later, on each of three
days-~Ju1y 15, August 15, and September 15.

On September 16, 2C0 rooted cuttings of each variety were
potted in 3 inch pots in the same soil mixture as used pre-
viously. They were placed in a coldframe and given partial
shade for about one month. On November 25, 150 of the most
uniform plants of each variety were selected out and given a

uniform pinching. Thirty-five plants of each variety, sel-

ected at random, were washed and dried to constant weight.

The remainder of the plants was arranged in a manner pre-
viously mentioned on a well lighted bench. The temperature
throughout the rest of this particular experiment was main-
tained at approximately 50°F. during the night, with slightly
higher day temperatures. Thirty-five plants of each variety
were dried December 27, January 27, and Harch l, which conclud-
ed this particular phase of the experiment. The plants re-
ceived the natural daylight during this period which was pre-
dominately cloudy, as shown in Table 8.

The second part of this experiment was an attenpt to de-
termine the comparative leaf efficiency of the three varieties
.by using the "twin- or Opposite-leaf" method of sampling des-
cribed by Denny (7). Carnations were found to have identical
opposite leaves.

In August, the three varieties were planted in alternating
rows in a 21 foot bench on the east side of a carnation house.
They were planted in the same soil mixture used for commercial
production.

In adapting the "twin-leaf" method of sampling to carna-
tions, it was first necessary to find some method of measuring
the leaf area. This was done by blueprinting 160 leaves of each
variety and measuring them with a planimeter. The area (y) of
each of these leaves was then plotted against the length (x)
and the curve of best fit derived by the method of least squares.

The resultant relationship was parabolic in type. The derived

equations for the three varieties were as follows:

leaf efficiency. Samples were taken under various light in-

tensities throughout January, February, and March.
Experimental Results

The average dry weights for the three varieties were ob-
tained on the dates shown in Table 1. The weights presented
are averages of 35 plants weighed individually on each date.

The dry weights were not taken at regular intervals of
time. However, as shown by Tables 2, 3, 4, 5, 6, and 7, they
were calculated to a weekly basis, in order prOperly to derive
and compare the relative growth rates of the three varieties.
For this procedure use was made of the familiar equation:

R / 100 = loge we - loge wl.
For convenience of calculation, this equation was given the
form:

R / 100 . 2.302585 log w2/ W1.
These symbols, with their correSponding values, were used in

the composition of the tables mentioned above.

-4.8888 + 6.476x - 0.6882x2
0.0169 + 0.327x + 0.016lx2

Morning Glow y

Maine Sunshine y
Pelargonium y'= -0.0081 + 0.388x . 0.0056x2
This made it possible accurately to determine areas on the
simple basis of measurements of leaf lengths.

Since the "twin-leaf" method of sampling on carnations
involves pulling the leaves from the stems with a downward
motion, it was necessary to calculate the approximate error
in sampling. Duplicate samples of 50 opposite leaves were
dried to constant weight and their weights compared. Five rep-
lications were made for each variety. The maximum error in-
volved in sampling wast1.67% for the Pelargonium variety,
30.77% for Morning Glow, and 10.44% for Maine Sunshine.

Samples were taken under different intensities of light,
which were obtained by using natural daylight, 5C0 watt, and
1000 watt Magda bulbs, during cloudy weather. The.lpwest
light intensities were obtained by shading with black cloth.
Light intensity readings were taken every hour by means of a
General Electric photoelectric galvanometer and an average of
these readings used as the light intensity for the daily per-
iod. Temperature readings were also taken and averaged in the
same manner.

In sampling, one of a pair of opposite leaves was taken
at 8 A.M. and the other taken at 5 P.M. Approximately 50
leaves were taken in each sample. After lengths of leaves
were measured for each variety, the samples were dried to con-
stant weight in an oven at 70°C. The increase in dry weight

over the 9 hour period was used as a basis for comparison of

Table l:

- 10 -

Dry Weight Averages of Thirty-five Plants
Weighed Individually

 

Date

 

 

 

 

 

 

 

 

 

 

 

van etx 6/15 _7/15 8/15 elli—
Morning Glow 1.059 1.85h 3.295 5.053
Maine Sunshine 1.u0u 2.207 3.630 5.252
Pelargonium 0.963 1.82M 3.16u n.553

Date

Varietr lizah ___;gug7. 11g: 311
Morning Glow o.usu 0.637 0.991 1.592
Maine Sunshine 0.601 0.652 0.9u3 1.579
Pelargonium 0.063 0.703 1.026 1.580

 

 

 

 

 

-11..

 

 

Table 2: Sumner Increase in Dry Weight for Homing Glow
Variety of Carnation

Date 6:01:36". '7', Log 3111 B/100 (3:6)
6/15 1.059
6/22 1.2u5 1.1756 0.07oh1 .1621 16.21
6/29 1.u31 1.1u9u 0.06032 .1389 13.89
7/6 1.617 1.1300 0.05308 .1222 12.22
7/13 1.803 1.1150 0.0u727 .1088 10.88
7/20 2.088 1.1581 0.06371 .1u67 1h.67
7/27 2.h13 1.16h3 0.06595 .1519 15.19
8/3 2.738 1.13H7 0.05500 .1266 12.66
8/10 3.063 1.1187 0.0u883 .112h 11.2u
8/17 3.u08 1.1126 0.0h650 .1071 10.71
8/2u 3.805 1.1165 0.0u766 .1097 10.97
8/31 n.202 1.1023 0.0h297 .0989 9.89
9/7 n.599 1.09u5 0.039u1 .0907 9.07
9/15 n.996 1.0863 0.03583 .0825 8.25

 

 

 

 

 

 

* Weekly increase in dry weight in percentage.

-12-

 

 

Table 3: Summer Increase in Dry Weight for Maine Sunshine
Variety of Carnation

Date .tf'f; 2:5.. :38; Log :38, 3/100 (Bite)
6/15 1.uou
6/22 1.592 1.1339 0.05u61 .1257 12.57
6/29 1.780 1.1181 0.08848 .1115 11.15
7/6 1.968 1.1056 0.0u376 .1008 10.08
7/13 2.156 1.0955 0.03981 .0917 9.17
7/20 2.836 1.1299 0.05308 .1222 12.22
7/27 2.757 1.1318 0.05385 .12h0 12.uo
8/3 3.078 1.116u 0.09766 .1097 10.97
8/10 3.399 1.10h3 0.0u297 .0989 9.89
8117 3.735 1.0988 0.0u100 .09nh 9.1a
8/2u h.101 1.0980 0.0u060 .0935 9.35
8/31 h.u67 1.0892 0.03703 .0853 8.53
9/7 “.833 1.0819 0.0338} .0779 7.79
9/1u 5.199 1.0757 0.03181 .0732 7.32

 

 

 

 

 

 

* Weekly increase in dry weigot in percentage.

-13-

Table ll: Summer Increase in Dry Weight for Pelargonium

Vari ety of Carnation

 

 

D... .3183. “81 “g "81 B/ioo (1922.)
6/15 0.963

6/22 1.16M 1.2087 0.08283 .1898 18.98
6/29 1.365 1.1727 0.06930 .1596 15.96
7/6 1.566 1.1u73 0.05956 .1371 13.71
7/13 1.767 1.1288 0.05231 .120u 12.0h
7/20 2.039 1.1539 0.06221 .1u32 18.32
7/27 2.3142 1.11486 0.06032 .1389 13.89
8/3 2.6h5 1.129u 0.05269 .1213 12.13
8/10 2.9u8 1.11u6 0.0h727 .1088 10.88
8/17 3.25u 1.1038 0.0h297 .0989 9.89
8/2u 3.568 1.0965 0.0u021 .0926 9.26
8/31 3.882 1.0880 0.03663 .08u3 8.u3
9/7 n.196 1.0809 0.033u2 .0770 7.70
9/1u n.510 1.07u8 0.03181 .0723 7.23

 

 

 

 

 

 

"' Weekly increase in dry weight in percentage.

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15—

14-

P"
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I

12-

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11—

b

10—

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RATE

 

 

- 14 -

Fig. 1: Rate of Growth of the Three Varieties
During the Summer Vonths.

Legend:
Morning Glow _______
Maine Sunshine --w-—w—

 

Pelargonium
Da‘m‘
: 1
' ' ' ‘ ' ' 8 .L 1 a
m 91 22 ._ 2‘ .2 2‘ - \g u) u) 0‘
‘8‘ 0 I‘- F- [- ts- w to m

9/1h'

-15-

The three graphs in Figure l have much the same charac-
teristics. All three varieties showed a rapid growth rate,
reaching a maximum the first week, then decreasing for 3 weeks,
then rising again during the sixth and seventh weeks, and fin-
ally showing a downward trend for the remaining 7 weeks. The
initial growth rate of the Pelargonium variety is significantly
higher than that of Morning Glow. However, beginning with the
sixth week, and throughout the remainder of the period, Morning
Glow exceeded Pelargonium. Throughout the experiment the growth
rate of the variety Maine Sunshine was significantly lower than
that of the other varieties, with the exception of the last four
weeks, when it slightly exceeded the growth rate of Pelargonium.
This may be explained by the fact that plants of the Maine Sun-
shine variety were in a somewhat hardened condition when received,
one month before the experiment was started. For the entire
period of 15 weeks, Morning Glow increased 477 per cent, and
Pelargonium increased 473 per cent, against 874 per cent for Maine
Sunshine. The light conditions prevailing during the 13 weeks

were sunny, as shown in Table 8.

- 16 -

Table 5: Winter Increase in Dry Weight for Morning Glow
Variety of Carnation

 

 

 

 

 

 

 

Date “in; 213%.. '36 Log W381 B/100 (11:; o)
11/28 0.888

312/1 0.516 1.0661 0.02776 .0639 6.39
12/8 0.588 1.0620 0.02612 .0601 6.01
12/15 0.580 1.0588 0.02889 .0568 5.68
12/22 0.612 1.0552 0.02325 .0535 5.35
12/29 0.660 1.0788 0.03262 .0751 7.51
1/5 0.780 1.1212 0.08961 .1182 11.82
1/12 0.820 1.1081 0.08858 .1026 10.26
1/19 0.900 1.0976 0.08060 .0935 9.35
1/26 0.980 1.0888 0.03703 .0853 8.53
2/2 1.097 1.1193 0.08883 .1128 11.28
2/9 “1.221 1.1130 0.08650 .1071 10.71
2/16 1.385 1.1015 0.08218 .0971 9.71
2/23 1.869 1.0922 0.03822 .0880 8.80
3/1 1.592 1.0837 0.03503 .0807 8.07

 

’ Weekly increase in dry weight in percentage.

-17-

Table 6: Winter Increase in Dry Ieight for Maine Sunshine
Variety of Carnation

 

 

Date a???) gyms. % Log “/26 200 (Hits)
11/28 0.601

12/1 0.612 1.0183 0.00787 .0181 1.81
1218 0.623 1.0180 0.00775 .0178 1.78
12/15 0.638 1.0176 0.00760 .0175 1.75
12/22 0.685 1.0173 0.00785 .0172 1.72
12/29 0.671 1.0803 0.01703 .0392 3.92
1/5 0.737 1.0988 0.08060 .0935 9.35
1712 0.803 1.0895 0.03728 .0857 8.57
1/19 0.869 1.0822 0.03823 .0788 7.88
1/26 0.935 1.0759 0.03181 .0732 7.32
2/2 1.055 1.1283 0.05231 .1208 12.08
2/9 1.186 1.1282 0.05077 .1169 11.69
2/16 1.317 1.1108 0.08532 .1088 10.88
2/23 1.888 1.0998 0.08100 .0988 9.88
3/1 1.579 1.0908 0.03783 .0862 8.62

 

 

 

 

 

 

"‘ Weekly increase in dry weight in percentage.

Table 7:

-13...

Winter Increase in Dry Weight for Pelargonium

Variety of Carnation

 

 

Date “inf; 22'... “381 Log $81 R/ 100 (Rite)
11/28 0.663

12/1 0.671 1.0121 0.00522 .0120 1.20
12/8 0.679 1.0119 0.00518 .0118 1.18
12/15 0.688 1.0133 0.00573 .0132 1.32
12/22 0.697 1.0131 0.00565 .0130 1.30
12/29 0.728 1.0387 0.01662 .0383 3.83
1/5 0.797 1.1008 0.08179 .0962 9.62
1/12 0.870 1.0915 0.03822 .0880 8.80
1/19 0.983 1.0839 0.03503 .0807 8.07
1/26 1.016 1.0778 0.03222 .0782 7.82
2/2 1.123 1.1053 0.08336 .0998 9.98
2/9 1.237 1.1015 0.08218 .0971 9.71
2/16 1.351 1.0922 0.03822 .0880 8.80
2/23 1.865 1.0888 0.03503 .0807 8.07
3/1 1.580 1.0788 0.03262 .0751 7.51

 

 

 

 

 

 

* Weekly increase in dry weight in percentage.

 

- 19 -

19!-

Rate of Growth of the Three Varieties
inter vonths.

During the w

Fig. 2:

15 -

17 -

Legend

 

hine-—~—-»—+

ow -_--_____
Pelargonium

orning GI
Maine Suns

a 9'
1'1

16'-

.. 1Jj|lulnll

15 -
fl4-

13 -

12‘-

11 -

I
’
'
. .’
I
I .
I
l
I
I
I
I

‘mnm

‘
.0
H
\
N

. m\m

1 N\m

 

o~\a

1 mH\H

I NH\H

-20-

Much less favorable light conditions prevailed when
samples were taken during the winter months. The results are
presented graphically in Figure 2. The growth rate of Morning
Glow increased rapidly, beginning with the first week and
reaching a maximum on the sixth week. Pelargonium and Maine
Sunshine grew very slowly until the beginning of the fifth week,
when they increased rapidly for two weeks. From the sixth week
on, Pelargonium followed the growth curve of Morning Glow, but was
significantly lower. However, the growth rate of Maine Sunshine
increased rapidly during the tenth week until it exceeded that of
Morning Glow for the last 5 weeks of the period. All three
varieties began a gradual decrease in growth rate during the last
5 weeks. For the entire periOd of 14 weeks, Morning Glow in-
creased 329 per cent, compared to 263 per cent for Main Sunshine
and 238 per cent for Pelargonium.

Since the plants were the same age and had identical treat-
..ment. Piaure 2 shows Morning Glow to be either a more rapid
starter, or else it was able to use more efficiently the lower
light intensities during the first 9 weeks of the period. The
more rapid rate of growth of the Maine Sunshine variety, during

the last 5 weeks, corresponds to an increase in average light

intensitv durina.that time.

-‘21 -

Table 8: Weather Data for Periods Covering
Growth Experiments*

 

 

 

Days Partly Hours of Per Cent
Month Clear Cloudy Cloudy Sunshine of Possible
June, 1939 6 13 11 302 66
July 1h 11 6 361 78
August 15 13 3 316 73
September 11+ 9 7 265 71
November 11 7 12 1% 50
December 3 8 2O 65 23
January, 19110 0 7 214 142 1h
February 7 2 20 95 31

 

Sunshine data.for the periods June to September, 1939, and
November, 1939, to February, l9h0, are presented in Table 8. Only
the last 6 days of November were included in the second period.

That there were comparatively few hours of sunshine in December
and January is easily seen. Not only was there an increase in num-
ber of hours of sunshine in February over the two previous months,
but also an increase in light intensity during the cloudy days.
Mid-day light intensity frequently dropped to 100-200 foot-candles
during December and January. The lowest corresponding intensity for

February was 315 foot-candles.

 

* Obtained from the United States Weather Bureau Station at East
Lansing, Michigan.

Table

9:

- 22..

Conditions of Light and Temperature

Low Light Intensities (in foot-candles)

Photosynthate Produced Under Different

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Light 35 86 59 6h 98
“rm" Temp.‘ 56.6 57.1 6n.2 69.0 72.5 ““1
Morning Glow -O.655 1.16” 0.988 0.898 -O.861+ 1.821
Maine Sunshine -O.382 0.1483 1.3452 -O.l36 -l.607 -0.l90
Pelargonium Go 180 .0062“.I -0e883 00 876 44. 11+) “he 59”
Medium Light Intensities (in foot-candles)
Light 5% 61:0 765 850 ‘ 970
"’1“? Twp.‘ 55.0 58.0 58.0 62.0] 66.3 ”“1
Morning 610' 10557 1051‘s 20775 100.4 3.109 10.030
Maine Sunshine 0e878 0e980 2.185 2065 1e555 8.25“
Pelargonium 0.918 3.065 2.813 1.676 l$.31} 12.785
Hig1er Lian Intensities (in foot-candles)
Light 1502 1615 20143 20173
“’1’” Tunp.‘ 62.2 59.0 67.0 67.0 Tm“
Morning 910' 3.982 6.082 6.256 7.123 23.723
Maine Sunshine 7.260 3.695 12.991 10.1487 311.163
Pelargonium 7 . 576 6. 395 10. 132 9. 365 33.1468

 

 

 

 

 

 

"' Temperature in degrees I.

-23-

The amount of photosynthate in grams per square meter of
leaf area, over 9 hour periods, is presented in Table 9. It is
at once apparent that temperature plays an important role in
photosynthate accumulation. Since it was not possible to keep
the temperature constant, samples were taken under different
temperatures as well as different intensities of light. The
low light intensities were obtained by shading with black cloth,
medium light intensities were obtained by use of 1000 and 500
watt Mazda lamps, and higher light intensities occurred during
partially cloudy weather in early March.

The total amount of photosynthate produced by a variety un-
der a series of light intensities, as presented in Table 9, is
of little significance, since each set of conditions within the
series is different. However, the efficiency of a variety un-
der a given set of conditions is exemplified somewhat in the
totals.

Under low light intensities, Morning Glow was the most ef—
ficient under almost every set of conditions.' Pelargonium seems
to be least efficient under the majority of light intensities
and temperatures tried. Temperature played a much more impor-
tant part when light was limited; its effect being most pro-
nounced on the_Pelargonium variety. With 98 foot-candles
average light intensity and 72.5°F.ytemperature, respiration
exceeded photosynthate production 0.864 grams for Morning Glow,
1.607 grams for Maine Sunshine, and 4.143 grams for Pelargon-
ium. 6

Under medium light intensities of 546-970 foot-candles

Pelargonium produced the largest amount of photosynthate.

-24-

Maine Sunshine produced the least amount under all conditions
tried, with one exception. With 850 foot-candles of light and
62 ° temperature, Maine Sunshine produced 2.656 grams of dry
material per square meter of leaf area, compared to 1.676 grams
for Pelargonium, and 1.046 grams for Morning,G10w.

Both Maine Sunshine and Pelargonium accumulated signif-
icantly more photosynthate at higher intensities than did Morn-
ing Glow.:

A close scrutiny of Table 9 reveals occasional errors,
which are difficult to eliminate entirely. The "twin—leaf meth-
od" of sampling, while adaptable to carnations, is one in which
many errors may be involved. The increase in dry weight is so
small over a 9 hour period that even the smallest error may be

accentuated.
Discussion

The.growth curves for the three varieties of carnations
used in this eXperiment correspond favorably to their production
records. During the summer months, when light is not a limiting
factor, relative growth rates were similar.

The relative growth rates for the three varieties during
the darker months were in the order of their productive ability.
Morning Glow showed a much higher growth rate than the other two
varieties and had a tendency to produce more new shoots in both
summer and winter. This higher growth rate for Morning Glow
may indicate only that the conditions of this experiment were
more suitable to the variety. It does not necessarily mean

that limited light was the sole cause of the slower growth

-25..

rates in the other two varieties. However, since growing con~
ditions of the experiment were those ordinarily given in com-
mercial production, it is possible to say that Morning Glow
exhibited the highest photosynthetic efficiency under these
conditions.

Evidence obtained from this experiment indicates that in
production of carnations, temperature becomes increasingly im-
portant when light intensity decreases. Under low light in-
tensities of 100 to 200 foot-candles, photosynthate production
may be so low that the amount of material respired easily ex-
ceeds that manufactured. This, in itself, may account for the
poor production and quality of flowers obtained by careless
growers.

Porter (ll) found that some tomato plants accumulated more
food than others under low light intensities. This is also true
of carnation varieties. The varietal differences in amount of
accumulated dry materials are probably due to differences both
in the rate of respiration and in rate of photosynthesis.

The response of the Pelargonium variety to temperature un—
der low light intensities indicates that it may be possible to
increase the quantity and quality of flowers on many low pro-
ducing varieties by growing them at still cooler temperatures.
Perhaps Pelargonium, and many other similar varieties, should
be grown at 45'F. during the cloudy months, while Morning Glow,

and similar varieties, may grow most favorably at 50 to SE'F.

- 26 -

Summary

A study of three typical varieties of carnations under

different light intensities reveals that:

1.

6.

Varietal differences in dry weight accumulation oc-
cur in carnations during periods when low light in-
tensity prevails.

During periods of higher light intensities, this dif-
ference in photosynthetic efficiency is less pro-
nounced.

Varieties showing a relatively high leaf efficiency
under low light intensities may be relatively less
efficient under higher intensities.

Carnations respond most favorably to light intensit-
ies of 1500 foot-candles or more.

Growing temperatures become increasingly important
with decreasing light intensities. When light inten-
sity drops to a certain point, respiration begins to
exceed carbohydrate accumulation. A decrease in tem-
perature tends to counteract the ill effects of lower
light intensities.

Some varieties may need cooler growing temperatures

than others when light intensity is limited.

5.

- 27 -

Literature Cited

Arthur, J. M., Guthrie, J. D., and Tewell, J. M. Some
effects of artificial climates on the growth and chemical
composition of plants. Am. Jour. Bot., 17: 416-482. 1930.
Blackman, F. F., Matthaei, G. L. C. Experimental re-
searches in vegetable assimilation and reSpiration. IV,

A quantitative study of carbon dioxide assimilation and
leaf temperature in natural illumination. Proc. Roy. Soc.
B, 76: 402-460. 1905.

Combes, R. Determination des intensités lumineuses optima
pour lee végetaux aux divers stages du developpement. An-
nalee des Sciences Maturelles, Bot. 9e series, 11: 75-254.
1910. '

Dastur, R. H., Mehta, R. J. A study of the effect of blue-
violet rays on photosynthesis. Ann. Bot., 49: 809-821.
1935.

Dastur, R. H., Samant, K. M. A study of the products of
photosynthesis in leaves in artificial and natural light.
Ann. Bot., 47: 295-304. 1933.

De Besteriro, D. 0., Durand, M. Influence de la lumiEre
sur l'absorption des matieres organiques du sol par les
plantes. Compt. rend. acad. sci., 168: 467-470. 1919.
Denny, F. E. The twin-leaf method of studying changes

in leaves. Am. Jour. Bot., 17: 818-842. 1930.

Hosterman, G. Kulturversuche mit elektrischen Licht.
Gartenwelt 26: 74-75, 1922. (From Bot. Abstr. 11: 383.
1922.)

10.

11.

12.

13.

14.

15.

-28-

Popp, H. W. Effect of light intensity on the growth of
Soybeans and its relation to the auto-catalyst theory

of growth. Bot. Gaz., 82: 306-320. 1926.

Porter, A. M. Effect of light intensity on photosyn-
thetic efficiency of tomatoes. Plant Physiol., 12: 225-
252. 1936.

Post, K. Results of experiments in floriculture which
have been made and are now in progress at Cornell Univer-
sity. (mimeographed copy--1939.)

Ramaley.p. Garyophyllaceous plants influenced in growth
and structure by artificial illumination supplemental to
daylight. Bot. Gaz., 92: 311-320. 1931.

Tinkler, M. A. H. The influence of the daily period of
light and the supply of potassium on the rate of growth of
tubers and other storage organs. Jour. Roy. Hort. Soc.
57:328. 1932.

Tjebbes, K. Der Einfluss des elektrischen Lichtes auf das
Pflandenwachstum. Landw. Jahrb., 56: 315-328. 1921.
(From Bot. Abstr. 10; 206. 1921.)

Withrow, R. B., Richman, M. W. Artificial radiation as a

means of forcing greenhouse crops. Ind. Sta. Bul. 380.

1933.

- 29 -

Acknowledgments

The writer wishes to acknowledge the helpful assistance
of Professor 0. E. Wildon in translating certain French articles
and to eXpress his appreciation of helpful suggestions and
criticisms offered by Professor V. R. Gardner, Professor J. W.

Grist, and Professor Wildon.

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