Plant Physiology (1957)
THE EFFECT OF SHORTENED DAY-LENGTH IN THE GERMINATION PERIOD
ON WATER RELATIONS AND ON ACCELERATION OF DEVELOPMENT IN MAIZE

N. S. Petinov and V. P. Ivanov
K. A. Timiryazev Institute of Plant Physiology, Academy of Sciences USSR, Moscow

Maize is a warm-weather plant in its biological preference, and is adaptable to cultivation under the shorter day-length conditions of southern regions. Under the conditions of northern regions its grain does not as a rule, reach maturity, and it is cultivated mainly for silage, and even then only to a limited degree. According to the data of Pisarev and Zhilkina [1], the existing early-maturing varieties of maize, particularly those of the Siberian type, when cultivated in the middle belt of the northern nonchernozem zone, while reaching wax stage of maturity, still give a relatively low yield both of ears and silage material — ear size is 12 to 15 cm, and ear weight is 40 to 50 g, while plant height is less than 1 m.

According to the data of Praksin [2], flinty varieties of maize, such as Voronezhskaya 6, Voronezhskaya 80, Chakinskaya Zhernchuzhina, Minunsinskaya, Bezenchukskaya 41, Beloyaroe Psheno, Pervenets Sibirsky, Spasovsky, et al., sometimes mature grain after the usual soil planting under the conditions of the Moscow Region, but give a low yield of grain, and particularly a low yield of green matter. Dent varieties, such as Partisan (Partizanka), Liming Kubansky, Krasnodar Hybrid 4 (Krasnodarsky Gibrid 4), Sterling, et al., have a long vegetative period and give an exceptionally high yield of green matter under the conditions of the northern nonchernozem zone, but ears do not mature under the usual conditions of cultivation.

When maize is introduced into the North, for its cultivation in the new regions it is necessary to select those varieties which are adapted to the soil, climatic, agricultural and economic conditions of such regions. With this purpose, an Investigation of 106 samples of native maize selections and 32 samples of foreign selections was carried out in 1950 at the Zonal Institute of Cereal Crops of the northern nonchernozem belt [1]. Under the climatic conditions of the summer of 1950, which was distinguished by temperatures lower than that of the average over many years, out of 37 short varieties of the Siberian type planted directly into the ground, only 6 to 7 varieties partially matured; in other varieties only individual ears matured. Out of the foreign varieties, only one Canadian variety gave three mature ears; other varieties from abroad gave no mature ears. Analogous results were obtained by the Moscow Regional Association of Agronomists (Dom Agronoma) and the Moscow Regional Agricultural Administration in testing maize varieties in 1950 under production conditions in a number of regions.

The data obtained in testing a large number of maize varieties, native as well as foreign, show that, under the conditions prevalent in 1950, even early-maturing varieties, when planted directly into the ground, do not assure one of obtaining mature grain in the middle band of the northern nonchernozem zone. However, it is known that from the biological point of view the best grain material is one which has been grown under the same soil and climatic conditions in which the farm planting takes place. In connection with this, one must acknowledge that little experimental study has been done up to the present, and insufficient experience in cultivation of maize for grain production in new regions has been accumulated.

A large number of books, brochures and scientific papers about the cultivation of maize in the northern nonchernozem zone have been published in the last few years [3-19], but almost all of them describe the experience of obtaining a high yield of silage material. Only in a limited number of papers [26-27] is there an attempt by individual scientists and agricultural specialists to solve the question of maize cultivation for grain in this zone.

The available scarce experience in maize grain production in the middle band of the northern nonchernozem zone indicates that, for successful solution of the problems involved, it is necessary to study more deeply the biological peculiarities of maize and its climatic requirements in the new regions.

In the northern nonchernozem zone warmth is the limiting factor among all the basic factors which are necessary for the normal growth and development of maize.

*1 centner = 50 kg.

Some of the investigators [20-31], taking into consideration the higher heat requirement of maize, as compared with other cereal crops, followed the practice of growing maize in peat-humus pots in the early stages of its development, in order to obtain mature grain under the conditions of the northern nonchernozem zone, Thus, at the Zonal Institute of Cereal Crops of the nonchernozem zone (Praksin [2]), in 1954 the maize variety Krasnodar Hybrid 4, planted on April 10 in peat-humus pots and later transplanted to soil, gave a high yield of mature grain (57 centners*/hectare), The variety Liming Kubansky, in the same conditions, did not mature, even when started in peat-humus pots.

According to the data of the Tulunskaya Selection Station (Malinowsky and Turchensky [28]), in 1954 in the lrkutsk Region the maize varieties Kharkov White Dent (Karkovskaya Belaya Zubovidnaya) and a hybrid between Pioner Gorsky and Voronezhskaya 76 gave a yield of mature ears when planted out as seedlings. Late-maturing maize varieties, such as VIR 42, Yellow Fling (Kremnistaya Zheltaya), Odesskaya 4, Odesskaya 10, and several others, gave a high yield of green matter, but no mature ears, even when planted out as seedlings under the conditions of the Tulunskaya Selection Station.

Eighteen varieties of maize were tested for the purpose of grain production at the Department of Selection of the Irkutsk Agricultural Institute in 1954 [28]. All 18 varieties were planted in small peat-humus pots on April 20, two seeds per pot. Ten days before transplanting to soil, the seedlings were hardened at low temperatures (3-5°). The seedlings were planted in soil on June 8. Ten early-maturing varieties reached wax maturity. Even after initial growth in pots, the late-maturing varieties, such as Sterling and Ivory-King (Aivori-King) towards September 1 matured ears only to the milk stage. According to the data of Praksin [2], the variety Partisan gave 800 centners/hectare of green material with ears in the 1953 tests of the Zonal Institute of Cereal Crops of the nonchernozem zone, and 940 centners/hectare in the tests of the State Farm "Gorki II." In 1954, the latter variety gave fully-mature grain toward the end of September under Podmoskovie conditions,

On the Gorky State Farm of the Moscow Region, maize planted as seedlings gave ears at the wax stage towards August 18 in 1954 [31].

In 1952, on the collective farm “Put Novoi Zhisni" of the Kuntsevsky District, Moscow Region, maize seedlings which were grown in peat-humus pots at the Zonal Institute of Cereal Crops of the nonchernozem zone, and transplanted to soil on June 10, gave no mature grain whatsoever towards September 15.

According to the data of the T. S. Kh. A. Experiment Station for Field Crops [3], seedlings of maize grown in peat-humus pots and transplanted to soil in 1954, a year of very favorable climatic conditions, gave a high yield of dry grain. However, in the same year (1954), on the State Farm "Karavaevo" in the Kostroma Region (Vetchinkin and Proshchalikin [7]), no fully-matured grain was obtained even when maize was planted as seedlings and given good care,

Chapman [32] carried out experiments with 50 varieties of maize under English climatic conditions. He also used the method of planting seeds in peat-humus pots. The results of the experiment were that only two varieties out of 50 gave ears, and even those did not mature to the wax stage.

The literature survey shows that, for maturing maize to the wax stage, the usual seedling culture is not sufficient, particularly for the late-maturing varieties.

For the cultivation of maize for grain in new areas, along with selection of adapted varieties and use of the method of seedling planting, it is necessary to utilize all methods of affecting plants, to speed up their growth and development. One such method, according to the data of Balura [23], is vernalization of seeds, which speeds up the appearance of sprouts and the onset of flowering and of the milk-maturity stage at a temperature of 25°, and particularly with alternating day-night temperatures (day 25°, night 1°); the introduction of phosphorus fertilizers significantly accelerates the development of plants and the maturing of grain. Sokolev [27] notes a positive effect of drying maize seeds at a temperature of 35-40° on their planting qualities. Avakyan [20] held germinated seeds of midseason-maturing varieties of maize at a temperature of 2 to 5° for 5 to 10 days prior to planting them into soil. When planted, such seeds gave early and synchronous sprouts, resistant to low spring temperatures. However, ears in this experiment matured only to the milk-wax stage.

According to the data of Kuzmichev [11] and Gorshkov [39], after additional ripening of immature ears, hung in a well-heated building (15 to 20°), viable seeds were obtained (up to 83% germination), I. V. Yakushkin [3] includes various stimulators, such as treating maize seeds with manganese salts, among methods of accelerating growth and development of maize.

The development of maize is significantly accelerated by shortened day-length in the initial period of its development. Here one must mention that the prolonged photoperiodic reaction of plants to a brief treatment with a shortened day-length in the beginning phases of plant development was first established by Egiz [33], for soybeans and maize. Later, this phenomenon of photoperiodic after-effect in soybeans, kidney beans, mustard, and barley was shown in the experiments of Lubimenko and Shchlegova [34]. A detailed investigation of the problem of photoperiodic after-effect on plants was made by Razumov [35] in his experiments with millet and oats. Extensive and fruitful work in generalizing from the published data of many investigators, as well as in development of theoretical ideas concerning the photoperiodic reaction, was presented by Chailakyan [36, 37, and other papers]. The same purpose is served by a summary a paper of Samigin [38], in which a great amount of material on photoperiodism in plants is systematized.

The successful solution of a number of theoretical problems concerned with the photoperiodic reaction of plants led scientists to the idea that the scientific achievements in this field should be utilized for practical purposes, and particularly for the introduction of maize into the northern districts of the nonchernozem zone. Thus, for example, Avakyan [20, 21], in the course of a number of years, carried out work in the cultivation of early-maturing, midseason-maturing, and late-maturing varieties of maize on the experimental farm of the V. I. Lenin All-Union Academy of Agricultural Sciences, at "Lenin's Hills."

Until 1954, the maize on this farm was grown for silage, and only in 1954 were experiments set up for obtaining grain. With this purpose in mind, for shortening the photo-inductive stage, an artificially-shortened 10-hr day was applied from the moment of sprout appearance for 25 to 30 days. In this experiment, maize plants, variety Odesskaya 10, were grown in small peat-humus pots until transplantation into soil. By September 10, part of the ears were harvested for seeds. The rest of the ears were harvested in the milk-wax stage for silage, together with the green material.

It can be seen from the survey of the literature that maize in the northern nonchernozem zone was grown mainly for silage until 1954.

In 1954, individual investigators set up experiments with the aim of obtaining mature grain of maize by planting seedlings as well as by planting directly in soil. However, the meteorological conditions of 1954 in the northern nonchernozem zone were exceptionally favorable for the growth of maize, as compared with the average of many years. Also, the maize varieties which were used for the experimental investigations were often selected at random and without consideration of their suitability for this zone. Because of that, these results in 1954 are not characteristic. Taking this into consideration, in 1955 and 1956 we took as a problem the obtaining of mature grain of early-maturing maize varieties in the Moscow Region, under the climatic conditions usual for this zone, by means of treating young plants with a shortened day-length.

METHODS

In 1955, two varieties of early-maturing hybrid maize were used for experiments: R-3 and B-271, produced at the Institute of Genetics, Academy of Sciences USSR; in 1956, three late-maturing varieties were included in the experiments in addition; Sterling, Krasnodar 1/49 (Krasnodarsky 1/49) and Partisan. The latter variety may be better referred to as midseason-to-late in maturing. In the first year of the experiments the dry seeds, treated with hexachloran, were planted on May 10 in small peat-humus pots, which were placed in flats (12 x 40 x 60 cm in size). Seventy peat-humus pots were placed in each flat. A layer of river sand 5 cm thick was placed in the bottom of the flat, and on it a layer of hotbed soil was placed so that the tops of the peat-humus pots were level with the top of the flat. After planting the seeds, the flats were watered with tap water to 60% of the full water-capacity of the soil. This moisture percentage was maintained throughout the whole experiment. The fiats, planted with maize, were placed in a greenhouse where the air temperature was held at 25 to 28°. Synchronous sprouts appeared in variety R-3 on the sixth day after planting, and on the seventh day in variety B-271. After appearance of sprouts, half of the flats were left on the natural day-length, and the other half were covered with light-tight chambers (wrapped with heavy black paper) at 6: 00 PM and were uncovered at 8:00 AM. The experimental plants were covered daily up to and including May 29. Thus, the plants of variety R-3 in these flats were kept on the ten-hour day-length for 13 days, and those of variety B-271, for 12 days.

On June 1, all plants, those on natural day-length as well as those on the shortened 10-hour day, were planted into soil, 40 cm apart in the row, in rows 60 cm apart, in a three-fold replication. During the vegetative period, observations were taken of the growth and development of the plants, and samples of plants were also taken for analysis, according to the planned program of the investigation.

In 1956, the experiment was carried out on the same plan, but the number of days of shortened day-length was increased from 12-13 days to 28 days. Correspondingly, the seeds were planted in peat-humus pots on April 25, In all treatments, synchronous sprouts appeared on the eighth day. Seedlings were transplanted into soil on May 31.

EXPERIMENTAL RESULTS of 1955

Phenological observations showed that plants receiving a 10-hour day-length in the initial period of their development formed their reproductive organs much faster, as compared with plants on the natural day-length (Table 1).

TABLE 1
Time of Appearance of Reproductive Organs and Development of Grain in Maize Exposed to Various Cultural Conditions.
Experiment of 1955 After Young Plants Were Exposed to Various Cultural Conditions, Experiment of 1955

  Variety R-3 Variety B-271
Stage of development natural day-length 10-hr day-length natural day-length 10-hr day-length
Beginning of appearance of florets:
Male Aug. 10 Aug. 3 Aug. 11 Aug. 6
Female Aug. 15 Aug. 9 Aug. 17 Aug. 11
Mass flowering:
Male Aug. 13 Aug. 7 Aug. 14 Aug. 8
Female Aug. 18 Aug. 12 Aug. 20 Aug. 14
Wilting of silks: Aug. 24 Aug. 19 Aug. 25 Aug. 21
Milk stage of grain Sept. 7 Aug. 31 Sept. 9 Sept. 2
Milk-wax stage Sept. 18 Sept. 10 Sept. 20 Sept. 12
Completely wax stage Sept. 27 Sept. 19 Sept. 30 Sept. 21

From the data of Table 1 it can be seen that, as a result of the 10-hour day-length treatment for the first 12-13 days after sprout appearance, all phases of development were 6-8 days faster in both variety R-3 and B-271.

At the same time it is necessary to note that in the experiment of 1955 the acceleration of plant development by the short (12-13 days) treatment with shortened day-length did not have any significant effect of decreasing growth toward the end of the vegetative period. The increase of the period of treatment with 10-hour day-length from 12-13 days to 28 days significantly speeds up the development of plants, but at the same time sharply decreases all growth processes, as will be seen from the data of 1956.

In passing, we may remark that, insofar as meteorological conditions were concerned, the spring of 1955 in the Moscow Region was very unfavorable for the growth and development of maize (in the first half of June, after transplanting the plants into soil, the weather was cold). The autumn, on the contrary, was exceptionally favorable for the maturation of grain.

The aim of our experiment, as mentioned above, was the obtaining of ears matured to wax stage. Therefore, in order not to permit weakening of the main stem, we removed tillers, of which the development after various experimental treatments is given in Table 2.

TABLE 2
Effect of Shortened 10-Hour Day-Length in the Seedling Period on Formation of Tillers in Maize
(Average of Three Replicates, 66 Plants in Every Treatment of Experiment). Tillering June 25, 1955*

Variety and day-length Number of plants
with tillers
Total number
of tillers
Total weight
of tillers in g
Average weight
per tiller in g
Variety R-3
Natural day-length 32 63 1478 23.3
10-hour day-length 22 47 2490 53.0
Variety B-271
Natural day-length 9 21 229 10.9
10-hour day-length 21 52 2050 38.0

*Analogous data were obtained in the 1956 experiment.

*In all cases, the ears were weighed at once after removal from the plants.

From the data in Table 2 it can be seen that variety R-3 grown on the natural day-length in the seedling period gave a large number of plants with tillers, as compared with those grown on 10-hour day-length. In variety B-271 this correlation was not observed. Thus, according to our two-year data, the tendency of maize plants to form tillers depends not only on the day-length, but on varietal differences. However, the growth and development of tillers is determined first and foremost by the day-length. Thus, for example, at the time of tiller removal, the average weight per tiller of variety B-271 on natural day-length was 10.9 g, while on 10-day length it was 38.0 g, almost four times as great. In variety R-3, the average tiller weight was correspondingly 23.3 g and 53.0 g, i.e, was more than two times greater in the plants on 1-hour day-length. In plants of variety R-3 from which tillers were removed, individual ears reached the full wax stage on September 11 in the 10-hour day-length series, while in the natural day-length series, they reached it on September 17. In the former case, out of 66 plants, two gave single ears weighing 218 g and 277 g, and one plant gave two ears weighing 191, and 228.9 g. In the latter case (six days later), three plants gave single ears weighing 138.5 g, 152.7 g, and 182.1 g.*

TABLE 3
Yield of Ears in the Wax Stage in Maize After Young Plants Were Exposed to Various Cultural Conditions.
Average of Three Replicates, 66 Plants Per Replicate. Data of 1955*

Variety Natural day-length** 10-hour day-length***
Total number
of ears
Average number
of ears per plant
Total weight
of ears in kg
Average weight
per ear in g
Total number
of ears
Average number
of ears per plant
Total weight
of ears in kg
Average weight
per ear in g
R-3 156 2.03 35.7 228.8 184 2.7 47.4 257.5
B-271 172 2.5 56.7 347.0 193 2.8 76.0 394.0
*In 1956, in connection with a sharp acceleration of development in plants given 10-hour day-length, and decrease of their vegetative mass, as compared with the data of 1955, there was no noticeable difference in the yield of ears in plants given shortened and natural day-length; even the reverse relationship was observed.
**Harvested on September 27.
***Harvested on September 19.

In variety B-271 given 10-hour day-length, the first ears reached full wax maturity on September 13 in two plants, one ear on each, weighing 356 g and 381 g. In plants given natural day-length, an ear reached the same stage of maturity on September 19, and weighed 347 g.

The shortened 10-hour day given in the seedling period not only accelerated development of plants by 6-8 days (see Table 1), but also increased the ear weight, as compared with plants given natural day-length (Table 3).

As can be seen from the data of Table 3, the average number of ears per plant in the natural day-length series was 2.3 in variety R-3 and 2.5 in variety 8-271. After exposure of these varieties to 10-hour day-length in the first days of seedling growth, the average ear number increased by 17.4% in variety R-3, and by 12% in variety 8-271, as compared with plants of the natural day-length series. In the 10-hour day-length series, the average weight of ears was also a little higher in both varieties.

EXPERIMENTAL RESULTS OF 1956

In the 1956 experiments the number of maize varieties was increased to five. Besides the two midseason-maturing varieties, R-3 and B-271, which were grown in 1955, three additional varieties were included in the experiment: two late-maturing varieties — Sterling and Krasnodar 1/49 and one midseason-to-late — Partisan. The time of treatment with shortened day-length was increased in 1956 to 28 days, and the program of the investigation was significantly widened.

Fig. 1. Development of reproductive organs (tassels) in various varieties of maize — R-3, Partisan, and Krasnodar 1/49 — on the twentieth day after transplanting seedlings into soil: 1 and 2) variety R-3; 3 and 4) variety Partisan; 5 and 6) Krasnodar 1/49. In the last variety, two plants were taken, because of the insignificant development of the tassels. 1, 3, and 5) Plants exposed to 10-hour day-length for 28 days after appearance of sprouts; 2, 4, and 6) plants which were left on the natural day-length throughout. The plants were analyzed before tassels emerged.

In reporting the results of investigations carried out in 1955, the comparable data from the experiments of 1956 were also noted. Therefore, in order to economize space, only the experimental material which supplements the previously-given data, or which is in some way contradictory to the experimental data of 1955, is presented in this section.

At the same time, it is necessary to note that, while in 1955 only the spring was unfavorable for the cultivation of maize, in 1956 the entire vegetative period was unfavorable; the autumn, with its early frosts, was especially unfavorable.

From the 1955 results described above, we know that treatment of midseason-maturing varieties of maize, R-3 and 8-271, with 12-13 days of shortened day-length in the early period of growth accelerates all phases of development, without any noticeable decrease in growth. The increase of the number of days of treatment to 28 greatly accelerates development of these varieties, while sharply decreasing their growth. Late-maturing maize varieties, such as Krasnodar 1/49 and Sterling, reacted to shortened day-length to a much smaller degree, as compared with the midseason-maturing varieties R-3 and B-271; variety Partisan occupied an intermediate position.

Figure 1 shows the development of reproductive organs of three varieties of maize: one midseason-maturing — R-3, one midseason-to-late maturing — Partisan, and one late-maturing — Krasnodar 1/49.

In order to study in greater detail the reaction of different maize varieties to shortened day-length, we carried out phenological observations on growth and development of plants throughout the entire vegetative period, height measurements were taken, and analyses of water relations were made.

TABLE 4
Dynamics of Growth (in cm) of Various Varieties of Maize Exposed to Shortened (10-Hour) and Natural Day-Length.
Average of 66 Determinations

Variety Treatment* Date of plant measurement
6/10 6/20 6/27 7/4 7/12 7/19 7/30 8/10 8/1
R-3 I 20 42 76 94 110 124 124 124 124
II 24 52 67 89 108 149 172 172 172
B-271 I 18 29 47 73 102 114 114 114 114
II 19 32 49 65 96 129 157 157 157
Partisan I 20 38 72 100 142 158 199 228 228
II 21 42 75 104 140 163 195 235 247
Sterling I 26 58 103 137 152 174 185 190 190
II 29 67 121 151 164 183 203 234 260
Krasnodar 1/49 I 24 41 76 112 145 163 184 186 189
II 25 42 79 133 152 164 178 210 210

Note. I) 10-hour day-length, for 28 days after appearance of sprouts; II) natural day-length throughout.

TABLE 5*
Dynamics of Total, Free, and Bound Water, Concentration of Cell Sap, Suction Force, and Osmotic Pressure
in Maize Plants Grown on 10-Hour Day-Length for 28 Days in the Initial Period of Development (Experimental)
and left on the Natural Day-Length Throughout (Control)

Indicators of water ratios July 6 July 16 August 9
expt. control expt, control expt. control
Variety R-3
Total water content in % 73.08 73.0 68.99 72.30 67.12 71.20
Amount of free water in % 58.40 61,20 47.14 52.94 38.94 43.28
Amount of bound water in % 14.68 11.81 21.85 20.64 29.0 28.08
Concentration of cell sap in % 11.40 9.0 9.80 8.0 13.60 11.40
Suction force in atmos 12.69 9.58 9.58 8.13 14.31 11.11
Osmotic pressure in atmos - - 19.82 19,0 22.12 20.26
Variety Partisan
Total water content in % - - 73.70 76.0 70.35 72.85
Amount of free water in % - - 54.68 61.90 45.40 4920
Amount of bound water in % - - 19.0 15.10 24.95 23.65
Concentration of cell sap in % - - 7.80 6.40 10.80 9.20
Suction force in atmos - - 8.13 6.70 9.58 8.13
Osmotic pressure in atmos - - 18.0 17.90 18.22 18.10

* The data of this table were obtained with the direct participation of Research
Associate Z. A. Sinitsina and Junior Scientific Collaborator L. D. Prusakova.

To economize space, only the data on the most characteristic phases of plant development are given.

The effect of shortened day-length in the initial period of development on further growth, in relation to the variety, is seen from the data of Table 4.

Measurements of plants were made: prior to tassel emergence from the first internode to the tip of the last (the youngest) leaf; after tassel emergence from the first internode to the tip of the tassel.

From the data of Table 4 and Fig. 2 it is seen that, prior to emergence of tassels (dates of measurement are June 10 and June 20), maize plants of all varieties exposed to the action of shortened day-length are smaller in size than plants left on the natural day-length. However, their rates of development show the reverse relation, as can be seen from Figs. 1 and 3.

Fig. 2. Growth of plants of midseason-maturing varieties of maize R-3 (on the left, two hills, two plants each) and B-271 (on the right, two hills, two plants each) on the twentieth day after transplanting into soil: 1 and 3) plants exposed to shortened day-length for 28 days after appearance of sprouts; 2 and 4) plants left throughout on natural day-length.
Fig. 3. Ears of maize, variety R-3 (at the left) and variety B-271 (at the right): 1) grown on shortened 10-hour day-length; 2) grown on natural day-length. The former with fully-mature grain, the latter at the end of the milk-wax stage (after bringing the ears to 14% moisture, they look somewhat wrinkled).

In the period of tassel emergence (from June 27 until July 12) the growth of plants of midseason-maturing varieties of maize exposed to the action of shortened day-length surpasses that of the plants left on the natural day-length, but afterwards the latter (controls) not only catch up with, but considerably surpass, the treated ones. The later-maturing varieties react less to the photoperiodic stimulus than do the midseason-maturing varieties.

In connection with changes in the growth and development of plants affected by shortened day-length, we also studied the main indicators of water ratios, in particular: total, free, and bound water, as well as concentration of cell sap, suction force, and osmotic pressure. From the data obtained, a regular increase of all these indicators is apparent in all varieties investigated. For economy of space only the data for two maize varieties are given in Table 5: one midseason-maturing one (R-3) and one midseason-to-late (Partisan).

From Table 5 it is seen that, judging by the total water content and amount of free water, the hydration of leaves in both varieties of maize is significantly lower after treatment with a shortened 10-hour day than in plants throughout on natural day-length. A similar conclusion follows from the other indicators of the water relations of plants: greater values of suction force of leaves, osmotic pressure, and cell sap concentration, in the first case, and, on the contrary, decreased values in the second case. Such a characteristic of water relations In maize treated with a shortened 10-hour day-length ensures, to a certain degree, the acceleration of development and faster aging of the plants. A characteristic conditioning of the rate and duration of growth and development of plants, corresponding to their water relations, is also connected with varietal differences. Lower hydration was also observed in midseason-maturing variety R-3, which in all phases of development was 13-14 days faster, than the midseason-to-late variety Partisan.

SUMMARY

1. The midseason-maturing hybrid maize varieties R-3 and B-271, grown near Moscow (Lenin's Hills), and exposed at a young age to the photoperiodic action of a shortened 10-hour day-length (13 days in 1955), developed 6 to 8 days earlier than plants left on natural day-length, without a noticeable decrease in growth.

2. For plants of the same varieties, an increase in the exposure time from 13 to 28 days (in 1956) led to an even greater acceleration of development (from 6-8 days to 12-13 days), but at the same time caused a decrease in growth of more than one-third, as compared with plants left on natural day-length.

3. Late-maturing varieties of maize, such as Sterling and Krasnodar 1/49 were less affected by the shortened day-length than were the midseason-maturing varieties R-3 and B-271; the variety Partisan, while responding well to the shortened day-length by acceleration of development, at the same time was reduced only to a limited degree in growth and accumulation of vegetative material.

4. The effect of a shortened day-length was also reflected in the water relations of the maize: the values of suction force of cells, concentration of cell sap, and the osmotic pressure, as well as of amount of bound water, were increased. At the same time, total water content was decreased, and, what is particularly important, the amount of free water was lowered. All this indicates a lowering of the degree of saturation of the cell with water, as compared with plants kept on natural day-length, which to a certain degree conditions the contraction of the vegetative period of plants in general, and the acceleration of their development in particular.

LITERATURE CITED
* In Russian

  1. V. E. Pisarev and M. D. Zhilkina, Selekts. i Semenov (Selection and Seed Production) No. 9, 17, 1951.
  2. S. S. Praksin, Production of High Yields of Maize in the Moscow Region* ("Moscow Worker" Press, 1955),
  3. L V. Yakushkin, Results of Investigations on the Introduction of Maize into the Nonchernozem Zone* (T. S. Kh. A. Press, 1955).
  4. A. M. Arenyev, Maize in Podmoskovie, The Experiment of the Collective Farm "Put Novoi Zhisni", Kuntsevsky District, Moscow Region* ("Moscow Worker" Press, 1955).
  5. T. L Belash, Growing Maize in the Tula Region* (Tula Regional Press, 1954).
  6. N. L Belkin, "Experimental cultivation of maize under the conditions of the Yaroslavl Region," Trudy Yaroslavl s. -kh. Inst. Vol. 2, No. 2 (1955).
  7. M. N. Vetchinkin and A. M. Proshchalikin, "Our experiment in cultivation of a new freed crop," Collection, Maize Cultivation in the Kostroma Region* (from the experiments of outstanding farms, participation of V. S. Kh. V.) (Kostroma Book Press, 1955).
  8. V. P. Dadikin, "Experiments in the cultivation of maize in Yakutia," Vestnik Akad. Nauk SSR, No. 7, 108 (1955).
  9. S. F. Dolzhenkov, Zemlidelie, No, 5, 57 (1954).
  10. N. A. Drozdov, "Introduction of maize in the north," Priroda No. 4, 72, (1955).
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