A Dahlia Experiment Almost No One Has Seen

How a 1951 Soviet dahlia experiment split seeds, produced "twin plants," and opened a forgotten line of research

In the spring of 1951, a short paper appeared in Priroda, the popular science journal of the USSR Academy of Sciences, describing something I have not seen anywhere else in the dahlia literature. Two Soviet botanists reported that they had taken germinating dahlia seeds, cut them in half with a razor blade, and successfully regenerated matched pairs of living plants from the divided seeds. They called the results "twin plants." By the end of the season, they had produced fifty pairs, and then, as far as the accessible dahlia literature is concerned, the work seems to have disappeared.

The paper was by G. I. Rodionenko and E. I. Zaar, published in Priroda in 1951 under the title "Obtaining Twin Plants in Dahlias." I already had the citation in my notes, but the article itself took some digging. It was buried in a Soviet-era journal issue that is not easy to find through ordinary English-language search tools. Once I finally had the article in hand, it was clear this was not a practical propagation article, or a clever shortcut for making more dahlia plants.

An image of page 62 from Rodionenko and Zaar’s article in Priroda, 40(5)

It was a brief, two-page article with a specific research purpose: the authors wanted matched dahlia plants so they could study the influence of external conditions on the doubleness of dahlia blooms. The paper touches dahlia propagation, plant regeneration, breeding questions, and a politically charged moment in Soviet science that shaped what questions were even worth asking.

The authors began with dwarf dahlia seeds germinated on moist filter paper. The timing was critical: they selected seeds only after the root had just begun to emerge, when it was about 2 to 5 millimeters long. At that stage, the seed was active enough to grow, but still small enough to divide.

They removed the seed coat with forceps and cut the exposed germinating seed lengthwise between the two cotyledons using a razor blade wiped with alcohol. The cotyledons are the first seed leaves of the embryo. In a dahlia seed they are small and, unlike the large seed leaves of beans or many legumes, do not contain a large reserve of stored food, which made the operation delicate.

Rodionenko and Zaar specifically noted that cutting between the cotyledons worked better than cutting through them. It created a smaller wounded surface, and the cut area closed more quickly with callus, the undifferentiated wound tissue that, in plants, can sometimes reorganize and produce new shoots or roots.

After cutting, the two halves were placed cut side up on filter paper moistened with water lightly colored by potassium permanganate, almost certainly as a mild disinfectant on freshly wounded tissue. The seed halves were kept in a covered crystallizing dish, with a 40-watt electric lamp supplying supplemental light for 14 to 16 hours per day. The temperature in the dish stayed around 16 to 18°C (61 to 64°F), rising to about 25°C (77°F) when the lamp was on.

The sequence they describe is striking. By the second day after cutting, the surface of the cotyledons began to turn green. By the third or fourth day, visible swellings appeared at the cut surfaces, and from those calluses new growing points and roots later formed. In some cases, two or three shoots developed from a single callus. After about a week and a half to two weeks, the regenerated plants were ready to move into soil, either in a frame or in greenhouse pots.

The experiment began on February 15. The twin plants were planted outdoors on May 14, and by the end of the summer the authors reported fifty pairs of dahlia plants from divided seeds, all developing normally.

Rodionenko and Zaar were not dividing established seedlings. They were dividing the germinating seed itself, at the moment when the root had only barely emerged, then coaxing two functioning plants from wounded embryonic tissue. A dahlia grower can imagine taking cuttings, dividing tubers, or even grafting dahlia shoots. This was something different.

A plate illustrating dahlia grafting techniques from the 1843 book The Dahlia: History and Detailed Culture According to the Advice and Procedures of the Best Growers by Augustin-Claude-Simon Legrand

Rodionenko and Zaar were not trying to invent a new way to multiply dahlias. They wanted experimental controls.

In ordinary seed-grown dahlias, every seedling is genetically different. That is one of the joys of breeding dahlias, and also one of the frustrations. If two seedlings differ in flower form, plant habit, color, vigor, or timing, it can be hard to know how much of that difference comes from genetics and how much comes from growing conditions. Rodionenko and Zaar wanted pairs of plants that began as nearly alike as possible, so that one plant could serve as the comparison while the other was subjected to some external treatment.

A breeder might reasonably ask why cuttings would not have served that purpose. Two cuttings from the same parent plant are genetically identical, and dahlia growers produce them routinely. But the authors were explicit that they needed plants matched not just in hereditary constitution but at the earliest stage of development, still in what they called the cotyledon phase.

A cutting taken from an established plant has already passed through weeks of growth, differentiation, and environmental response before it ever becomes a viable propagule. The twin-plant technique gave them something cuttings cannot: two plants of matched genetics that were both starting from zero, so that any experimental treatment would be acting on comparable material across the entire developmental arc from seedling to flower.

The specific question they were preparing to study was the influence of external conditions on the doubleness of dahlia inflorescences: whether conditions could affect whether a dahlia flower developed as more single, semi-double, or double. The 1951 paper does not give us those results. It gives us only the method for making the matched plants. They made the twin plants, grew them outdoors, and had fifty pairs by the end of summer. What they found when they compared flower form is not recorded in any source I have been able to locate.

Figure 2 on page 62 of Rodionenko and Zaar’s article in Priroda, 40(5)

It would be easy to classify this as tissue culture, but that framing does not quite fit. There was no sterile growth medium, no hormone-balanced agar, no flask culture, and no controlled laboratory regeneration protocol in the modern sense. Rodionenko and Zaar were using simple materials: filter paper, forceps, a razor blade, potassium permanganate, a glass dish, and an electric lamp.

At the same time, this was more interventionist than ordinary seed germination or classical embryology. They physically wounded and divided the germinating seed, then relied on callus formation and regeneration to restore a shoot and root system. The method falls between ordinary propagation and modern tissue culture: a low-tech regenerative experiment that demonstrates something most dahlia growers never have reason to think about. Under the right conditions, a tiny piece of wounded germinating dahlia tissue can reorganize itself and produce a complete plant. Not a technique anyone should rush out and try, given the narrow timing, the small tissue, and the likely failure rate, but as a demonstration of what dahlia embryos can do under the right conditions, it is not easy to forget.

The paper appeared in Priroda, which means "Nature." It was not a specialist dahlia journal or even a specialist botanical journal, but a long-running popular science journal associated with the Russian Academy of Sciences, founded in 1912 and aimed at a scientifically literate audience. That helps explain the form of the article: short, practical, and illustrative, including figures showing the apparatus and the seed halves, reading more like a demonstration of an experimental method than a full scientific paper.

But the date matters. The article appeared in 1951, during one of the most difficult periods in Soviet biology. Trofim Lysenko's influence over Soviet agricultural and biological science had reached its height, and three years before this paper appeared, the 1948 session of the Soviet Academy of Agricultural Sciences had denounced Mendelian genetics and led to the dismissal of thousands of scientists who had practiced it. Research involving heredity, environment, and the directed alteration of plants carried political meaning that it would not have carried in the same way elsewhere.

Rodionenko and Zaar open their article with language about the "directed alteration of plant nature," and that phrase is not a neutral description. It belongs to the scientific vocabulary of that Soviet moment. The experiment is interesting enough to stand on its own, and I have tried to let it do that here.

But the context does help explain why an experiment on external conditions and flower form had special resonance in 1951 Soviet biology. The question of whether the environment could reshape plant traits was not merely a technical question. It sat inside a much larger argument about heredity, development, and what kind of biology was politically acceptable. That does not tell us what Rodionenko personally believed; it tells us something about the room in which he was writing.

The cover of the March 1951 issue of Priroda containing Rodionenko and Zaar’s article

Around the same broad period, dahlia genetics was being studied in a very different way in the West. At the John Innes Horticultural Institution, W. J. C. Lawrence was using dahlias to study flower color, cytology, species relationships, polyploidy, and inheritance. His 1929 paper, "The Genetics and Cytology of Dahlia Species," begins as an effort to explain unusual distributions of flower color in dahlias, using controlled crossing and cytological study. In 1935, Lawrence and Rose Scott-Moncrieff published "The Genetics and Chemistry of Flower Colour in Dahlia," a much larger study focused on flavones, anthocyanins, pigment chemistry, and the genetic factors controlling color expression in Dahlia variabilis.

Those papers are not direct counterparts to the doubleness question Rodionenko and Zaar were preparing to investigate. Lawrence and Scott-Moncrieff were working on color, not flower form. But the two bodies of work represent something worth noticing side by side: Lawrence built his dahlia genetics around controlled crosses, cytology, polyploid inheritance, and biochemical analysis, while Rodionenko and Zaar were framing an experiment around environmental influence on development. Both used dahlias as experimental plants. They were working inside very different scientific frameworks, and in very different political worlds.

Lawrence and Scott-Moncrieff's dahlia work did not disappear after 1935. In 1946, Georg Melchers used their Dahlia variabilis results as an example of gene-dose effects in polyploids, showing that the work still circulated in European genetics after the war.

Plate XII from page 158 of Lawrence’s 1929 article “The Genetics and Cytology of Dahlia Species” in Journal of Genetics, 21(2)

Georgi Ivanovich Rodionenko later became a significant Russian botanist, but not primarily as a dahlia researcher. His lasting reputation was in Iridaceae, especially iris taxonomy and systematics, and he worked at the Komarov Botanical Institute in Leningrad across a very long scientific life. There is no evidence that he continued publishing on dahlias after the early 1950s. The twin-plant work appears to have been an early side path in a career that moved firmly toward irises.

E. I. Zaar seems to have stayed with the problem longer. While Rodionenko supervised the early work, Zaar carried the research line forward. A 1955 paper by Zaar in Trudy Botanicheskogo Instituta confirms that he continued publishing on the production of twin plants from cut seeds, apparently expanding the methodological work first described in the 1951 Priroda note. By 1961, Zaar had published a more developed physiological experiment in Botanicheskii Zhurnal on light conditions and meristem regeneration, a line of work that appears closely related to the earlier twin-plant experiments. The 1951 Priroda article did not disappear. It disappeared from the English-language dahlia literature, which is a different thing entirely.

Rodionenko and Zaar did not claim to have invented the general idea of twin plants from divided germinating seeds. They cited an earlier 1940 report by M. A. Nikonenko in Yarovizatsiya, describing "twin plants" obtained from larger seeds, apparently in legumes. Earlier still, M. D. Danilov had reported similar results with oak in 1930, and A. Sereisky with soybean in 1933. Yarovizatsiya was closely associated with Lysenkoist biology, and several of those cited papers have proven difficult to locate, which makes the Rodionenko and Zaar article feel like a surviving fragment from a larger, mostly inaccessible conversation.

They were adapting a known idea to dahlias, but dahlias were harder material. Their seeds were smaller, their cotyledons had less stored food, and the operation had to be done earlier and more carefully. In that sense, the paper is not just a report that someone cut a seed in half. It is a report that dahlia embryos, despite their small size and limited reserves, could survive this kind of surgical division and regenerate into normal plants.

Zaar's 1961 paper makes explicit where dahlias stood in that larger Soviet tradition: the 1950 to 1953 work at the Botanical Garden of the Botanical Institute of the Academy of Sciences of the USSR produced twin plants across twenty species from different families, and dahlia was singled out as showing the greatest regenerative capacity of all.

Page 557 from Zaar’s 1961 article in Botanicheskii Zhurnal, 46(4)

The 1961 paper "The influence of duration of illumination and spectral composition of light on the regenerative activity of the meristem of the shoot growing point" opens with a question that follows directly from the twin-plant method: once you have two genetically matched plants starting from the same developmental moment, what can you learn about the factors that control regeneration itself? Zaar had already observed, in the earlier work, that the number of growing points forming on a divided seed half was not always one. Sometimes two or three appeared on a single half, and in dahlia the regenerative response had been strong enough that four twin plants could be obtained from a single embryo, with each quarter of that embryo capable of producing up to five growing points.

The method was already in hand. The question became what drives that kind of response.

Zaar chose illumination as the first variable to test. In March 1957, using the same basic setup as the 1950 to 1953 experiments, sets of 150 to 200 divided dahlia seed halves were held under five different light regimes, ranging from continuous darkness to continuous light, with intermediate photoperiods of 12, 16, and 20 hours.

The results were not a simple gradient. Continuous light produced the worst outcome among the illuminated variants, with only 5 percent of halves forming double growing points. Continuous darkness caused about 70 percent of halves to die or fail entirely. The best result came from 20 hours of light combined with 4 hours of darkness, which produced double growing points on 42 percent of halves, and triple growing points on a small additional fraction. Alternating light and dark mattered; the rhythm of the cycle, not simply the quantity of light, was doing something.

The second series of experiments tested spectral composition. Using water filters to isolate different wavelength ranges, Zaar found that long-wavelength red light supported strong meristem activity and double growing-point formation. Removing the infrared portion of the spectrum eliminated double growing points entirely, even when visible red light was present. 

Blue light was disastrous: nearly all halves died or failed. Zaar interpreted the red and infrared results as evidence that active meristematic function required that part of the spectrum, connecting the finding to contemporary Soviet research suggesting that red light favored carbohydrate synthesis while blue light favored protein synthesis. The interpretation carries the theoretical language of its time and place, but the experimental result itself is straightforward: spectral composition mattered, and mattered strongly.

Taken together, the two series show something more specific than the general claim that light helps regeneration. The degree and form of regeneration in divided dahlia embryos was sensitive to both the duration and the quality of the light they received.

Table 1 from page 559 of Zaar’s 1961 article in Botanicheskii Zhurnal, 46(4)

For propagation-minded growers, these papers are a reminder that dahlias are capable of more regenerative flexibility than our everyday practices reveal. Most of us encounter dahlia regeneration in familiar ways: tuber eyes breaking, cuttings rooting, damaged shoots resprouting, or sometimes callus forming on wounded tuber tissue. Rodionenko and Zaar were working much earlier in the life of the plant, at the germinating-seed stage, and still managed to obtain complete plants from divided material. The 1961 results go further: the number of growing points formed on divided embryo tissue varied with lighting conditions, which means the regenerative response itself was not fixed.

For breeders, the unanswered question from 1951 is still unanswered. How much of dahlia flower form is fixed by inheritance, and how much can be shifted by the conditions a plant experiences as it develops? Every breeder knows that seedlings can change dramatically from first bloom to later bloom, from one season to another, or under different growing conditions. That is not proof of environmental control of doubleness, but it is enough to make the question feel like a real one. 

The 1961 paper didn’t answer it either; Zaar had shifted focus from flower doubleness to meristem regeneration, and the original breeding question that motivated the twin-plant technique in the first place remains open.

The 1953 catalog cover of the American company Swan Island Dahlias

These are not articles that will change how anyone grows dahlias today. The technique is too delicate for practical propagation, the breeding question they raised was never answered in the accessible literature, and neither paper is long enough to stand as a major research contribution. But together they preserve something worth knowing.

Scientists, working from 1950 onward in Leningrad, were thinking seriously about how to separate heredity from environment in dahlia development, and that work continued long enough to produce real experimental results. Dahlia was not merely convenient material. It was, of twenty species tested, the best regenerator. And the regenerative capacity of a germinating dahlia seed, carefully divided at just the right moment, was not simply binary: it responded to light, responded to spectrum, and could produce one growing point from a divided seed half, or two, or three. Zaar reported four twin plants from a single embryo.

What looked at first like a lost one-off experiment is the visible entry point into a longer Soviet research line that the English-language dahlia literature has never encountered. For a flower most of us know through tubers, cuttings, and seedling rows, that is a remarkable thing to find hiding in a DJVU scan of a 1961 Russian journal.

The two primary sources for this article are:

Rodionenko, G. I., & Zaar, E. I. (1951). Obtaining twin plants in dahlia  Priroda, 40(5), 62–63.

Zaar, E. I. (1961). The influence of duration of illumination and spectral composition of light on the regenerative activity of the meristem of the shoot growing point. Botanicheskii Zhurnal, 46(4), 557–560.

Both articles were located through Russian-language journal archives with AI-assisted search support. The 1961 Zaar paper surfaced only after following a Cold War-era CIA index card into a Soviet journal archive, where the correct issue existed as a DJVU scan rather than a searchable PDF. English translations of both articles were prepared from the originals and checked against the article texts.

This article also draws on Lawrence's 1929 and Lawrence and Scott-Moncrieff's 1935 papers on dahlia genetics and flower color, Melchers's 1946 discussion of polyploid gene-dose effects, and contextual sources on Priroda and Soviet biology in the Lysenko period.