Foreword to Duchesne's strawberry drawings
Text published in : Staudt G., 2003. Les dessins d'Antoine Nicolas Duchesne pour son Histoire naturelle des fraisiers. Paris. MNHN, Ciref. 370 p.
Text reproduced with slight translation emendations.
Duchesne is undoubtedly the forerunner in the study of the biology of strawberries. He is also known as the author of the chapter on pumpkins in Lamarck's Encyclopédie méthodique. Apart from those qualities, scientific history also records that this gardener dared enter into a scientific controversy with Linné. And that is about all.
When preparing this contribution, I first thought that it would be difficult to be original in areas of scientific history which have been dealt with by so many scholarly works. Great was my surprise when I found that Duchesne was ignored by classical works, not only of the history of botany (Greene 1983; Morton 1981; Sachs 1892) but also of the history of biology (Vignais 2001) or of genetics (Roberts 1929). At best, Davy de Virville (1954) briefly mentions him, stating that the Histoire naturelle des fraisiers "can be considered as one of the 18th century's best monographs on cultivated plants." More recently, there has been an entry on Duchesne in the dictionary of Darwinism (Allorge 1996), but he owes it to having been mentioned by Darwin for his work on strawberries (Darwin 1879).
Was Duchesne therefore nothing more than a gardener specialised in strawberries? One just has to read the Histoire naturelle des fraisiers to realise that it is not the case. His book is made up of two parts, the first of which describes in detail the strawberries he grew and tries to reconstitute their origin, their history and their botanical relations. After those 314 pages, no less than 118 pages are devoted to "Particular remarks on several points related to general natural history". Several of those "remarks" are in fact the discussion and the theoretical conclusions that Duchesne draws from the description of the results of his observations and experiments. This is a strikingly modern approach.
This point is discussed in Remark III. "On sexual separation in capitons and other plants". To appreciate Duchesne's discoveries, one should consider them in their historical context. Although the existence of sex in plants seems obvious to us today, few of our contemporaries, apart from some historians of science, realise that this is an 18th century scientific discovery. Indeed, it had been known since ancient times that the date palm was dioecious and that artificial pollination increased date production. But that was the exception proving the general rule which considered sex as one of the attributes of animals. This ignorance of plant sexuality did not prevent the development of botanical gardens and plant collections. Surprisingly, the creation of numerous tulip varieties during the "tulip craze" in the Netherlands and France does seem to result only from the reunion of numerous tulip types in collections, bees being the pollinating agent. Then, one just had to sow the seeds and sort out remarkable individuals. But between the late 17th and 18th centuries, clever gardeners must often have guessed the role of pollen, which scientists were to demonstrate and record in writing.
The first pollinating experiments (on dioecious plants) were published in 1694 by Camerarius. One then hears of Bradley (1717) castrating tulips, and of Logan (1739) doing the same with corn. The first artificial crossing is said to have been carried out by Thomas Fairchild on Dianthus in 1719. Besides, Miller (1751) also observed the role of bees and Gleditsch (1751) carried out pollinating experiments on Chamaerops and other dioecious plants. In France, one should also note the publication of Vaillant (1717). But not until Kölreuter (1760-1766) were all those experiments synthesised and confirmed (Morton 1981; Roberts 1929).
Throughout that period, actual experiments were strikingly few, and far less important than philosophical reasoning. Botanists seem to have accepted fairly quickly the idea that plants had a sex, by analogy with animals, but without trying to draw all the practical conclusions. Linnaeus' attitude is typical in this respect, since he precisely founded his classifying system on the characteristics of plants' sexual organs. But in his Philosophia Botanica (1751), Linnaeus places flower structure on the same leve! as "castration" (i.e. experimentation) among the elements arguing for plant sexuality.
Thus, Duchesne arrived at a time when the existence of plant sexuality was theoretically accepted and taught, but when the details of sexuality among species were hardly known. He had noticed that in his sowings of capron strawberries (Fragaria moschata), repeated for four successive years between 1760 and 1763, half the plants were "sterile" while the other half bore fruit. "I had already noticed, when examining their flowers, that the stamens of those sterile individuals being very strong, they were certainly excellent males; but I did not know that those of fertile individuals were totally impotent" (today we would say male-sterile). To prove this fact, Duchesne isolated a pot of female strawberry and checked that its stamens did not produce pollen.
The discovery of dioecy in strawberries came up against the morphological similarity of male and female flowers, which Linnaeus seems to have deemed sufficient to declare them to be hermaphrodites. This explains Duchesne's wordy efforts to reconcile dogma and reality: "Thus, sexes being always found together in the same flower, one can say that those plants are really bisexual by their nature, although the impotence of one or the other sex renders them unisexual in effect: the male individuals are but male hermaphrodites, while the others are female hermaphrodites: together, they could be called unisexual hermaphrodites." (Remarks, p. 30).
For 18th century botanists, plants were classiffed "by their nature", i.e. according to visible characters, and they found it difficult to take into account characters which could be observed only "in effect", which implied experimenting. Nowadays, only plants bearing both functional male and female organs are called hermaphrodites.
Nothing better illustrates the slowness in the diffusion of scientific discoveries and the weight of Linnean "dogma" than the fact that the dioecy of some strawberries was discovered again several times, both in England and in the United States. Fifty years after Duchesne, the Englishman Michael Keens (1817-18) wrote: "There are many different sorts of Hautboys: one has its male and female organs in the same flowers and bears abundant fruit; but the one I like best is that which contains the male organs in one flower, and the female in another [...]. I consider the right proportion to be one male for one female, to get an abundant yield. I learnt of the need to mix male plants with others by experience, in 1809; before that, I had chosen for my beds female plants only, and I was totally disappointed in my hopes for fruit. That year, suspecting my mistake, I got some male flowers which I placed in a bottle on the bed of female Hautboys ... ".
In the mid-19th century, sterility was still the main problem for strawberry growers in the United States. Wilhelm and Sagen (1974) have reported how an ignorant Cincinnati grower surprised his neighbours by getting yields five times higher than theirs. His secret lay in planting one bed of a pollinating variety after every seven or eight beds of a fruit-bearing variety. A committee named by the city's horticultural society had to investigate the case for two years before concluding in a report published in 1848 — and known in history as the Longworth Report — that strawberry varieties differed by the diversity of their floral biology. Significantly, the committee insisted on the fact that such "permanent freaks" contradicted Linnaeus' opinion on the normal condition of the genus Fragaria, and that almost all botanists had been content with reproducing Linnaeus' mistake without checking for themselves. Although American strawberry growers quickly put those discoveries to effect, many scientists still argued against them, leading Longworth ta answer in 1854 that "to understand the sexual character of the strawberry, I think one should leave Linnaeus aside, together with all great botanists and horticulturists, and carefully examine blooming plants and learn from ignorant market gardeners." And not until 1925 did a strawberry breeding specialist, Darrow, establish that strawberry sterility could also be due to environmental factors, such as spring cold.
The monophyllous strawberry and the species question
This is the subject of Remark II. "On the birth of the Versailles strawberry; and in this respect, on the distinction of species, races, and varieties."
The story of the Versailles strawberry is a well-known one: Duchesne saw it appear in 1761 in a bed of wood strawberry, and sent some specimens to Linnaeus. The latter did not hesitate to publish it under the species name Fragaria monophylla in his 1767 Systema Naturae. This strawberry, whose leaves had one blade instead of three, kept this character when multiplied by sowing, and greatly puzzled the young Duchesne. "How should it be considered, I then wondered? Is it a species? ... New ones get formed, then: is it but a variety? ... In other genera, how many varieties are considered as species? I was long in this alternative. [...] it appeared to me that there was something to correct in current ideas; but that the confusion was mainly caused by different authors applying the same words to totally opposite ideas." (p. 13-14) "This reasoning has led me to consider strawberries, altogether, as forming a species distinct from all others, and each particular strawberry as a race or a variety; it has also prompted me to investigate their genealogy." (p. 14) And Duchesne concludes: "This remark aims to deduce some general consequences concerning the distinction that must be made between the fixed and unchanging characters of species and the slight and changing differences between races; on the constancy of the former and the mutability of the latter." (p. 14)
After a philological analysis of the words genus and species, Duchesne shows how greatly naturalists have varied in their use of those words. "Instead of this word race, the word species is very often used; as a result, species have to be called genera ... " (p. 18-19). He adds that botanists, "being unable to ascertain whether the plants they spoke about were species, except by testing whether their differences changed when they were cultivated, they have often called species those which they could not examine, and they have given this name without balancing to all constant races. It is certain today that whereas species are stable, some races are also constant in their differences, while belonging to the same species: the Versailles strawberry whose birth I have witnessed, and which has become a race leader, dispels all doubts in this respect." (p. 21)
After this clear conclusion on the infraspecific status of the monophyllous strawberry, Duchesne states his method: "One must therefore look for means to surely distinguish races from species. The best would certainly be to carry out on plants, as on animals, the mating experiment; those which would produce fertile hybrids together would be stated to belong to the same species, whereas those which would refuse to do so would be considered as belonging to different species. It is to be hoped that similar experiments be carried out in great numbers." (p. 21-22) Once this criterion was established, Duchesne could apply it to other strawberries. After noticing that the "capiton" (Fragaria moschata) could not be fecundated by the "strawberry" (Fragaria vesca), he thus states: "it seems to me that one can hardly avoid considering the strawberry and the capiton as two actual species, despite their so close similarities, since the dog, fox and wolf are generally recognised as belonging to different species by their refusing ta mate together: I do propose to carry out, not only those fecundating experiments, but also all those which I will deem possible on other races, to make them produce hybrids" (Remarks, p. 40).
One can thus see that Duchesne had a very modern conception of the distinction between species and variety. After him, numerous botanists were to carry out abundant crossing experiments in order to lay the foundations of a rational classification of plants, and mainly of cultivated plants since the large numbers of cultivars made the task an urgent one. Nevertheless, Duchesne himself did not escape such confusion in the use of terms, at a time when biological terminology was not yet clearly distinct from common usage. In his own work, he begins his presentation of "different races" with a "description of the species" which is in fact that of the genus Fragaria: "before dealing with the details of their differences, it is worthwhile to consider them all together in the description of the species, that is to say of the ideal being which we substitute to all individual strawberries born and yet to be born."
Later, in 1790, the Strawberry entry he signed in Lamarck's Dictionnaire encyclopédique also begins with a "description of the species" and continues with that of "species" some of which are in fact species while others are varieties; moreover, all are given two-word species names.
The experimental method
Duchesne repeatedly insists on the need to experiment. In his first remark (p. 10), he criticises Miller for stating a presumption instead of experimenting. In his third remark, he concludes: "Cultivator botanists alone can try to carry out experiments so important for natural history, whether by sowing abundantly and observing carefully, or even by attempting to help nature to disfigure it, on this occasion, as Man has already done many a time to their advantage."
Duchesne was not content with experimenting, he was also keen on repeating his experiments several times before inferring conclusions: "delighted with this discovery, but well aware that one can hardly conclude from one single experiment, we endeavoured to repeat it immediately." Such practices are those of modern science.
Indeed, what is most striking is the confidence with which the young Duchesne dared contradict the practices of contemporary scientists. His critical assessment of the supposed hybrids reported by Linné is surprisingly outspoken: "would it not have been necessary to make sure the fact was possible through experiments? Yet he (Linnaeus) does not actually mention any." As for Linnaeus' veronica, "it would be most useful to attempt to repeat this fertilisation artificially, by pulling out the stamens of a sea veronica and fertilising it with verbena to see whether it would again give birth to a similar hybrid, and I am extremely surprised that Mr von Linné has not yet attempted to do so." (p. 58-59) Duchesne is one the pioneering gardeners who practised experimental botany at a time when botanists were often content with working on herbaria. In the 19th century, those gardeners were to become more numerous, to such an extent that the century has been called the "century of hybridisers". One of those hybridisers was of course Mendel with his peas.
Nevertheless, Duchesne seems to have limited his experiments ta castrating strawberries and planting pollinators beside them. He does not mention anywhere whether he took out pollen to place it on stigma. Neither does he seem to have thought of creating new varieties to produce strawberries. Not until the early 19th century, and especially Thomas Andrew Knight (1759-1853) who, according to Darwin, "operated over four hundred crossings on strawberries", was a new type of scientist to appear: the breeder.
An evolutionist vision
Duchesne lived in a French intellectual climate where the ideas of Buffon, Diderot and d'Alembert had forced the notion that plants and animals had a past, that they had changed in the course of time and would continue to change in the future. Duchesne was also immersed in the ideas of Adanson and of his teacher Bernard de Jussieu on plant classification. One can say with Allorge (1996) that in turn, his discoveries influenced Buffon, Adanson, Bernard de Jussieu and Lamarck.
It was rather early indeed, and Duchesne was cautious: "But if one allowed the imagination to build a system; this is, I believe, what one could say. One first individual, being perverted for some reason, was impotent at birth, that is, it bore aborted stamens; but, its pistils being uncorrupted, they were fertilised by the stamen dust of another similar individual, a perfect hermaphrodite... the individuals of subsequent generations, produced by those male hermaphrodites and those female hermaphrodites together, kept the same defect, according to the law of children's resemblance to their fathers and mothers; they formed a new race". This "system" imagined by Duchesne is in fact the principle of mutations and their persistence over generations.
For Duchesne, anyway, it was clear that all strawberries originated from one primeval species. That was why he thought of summarising the relations between strawberries in a "Genealogy of strawberries" which constitutes a phylogeny before the word had been invented. He does seem to be the first to have thus formalised the relations (which we would call genetic relations) between taxa (Barsanti 1992).
Old-time botanists attempted to size their drawings into an upright rectangle, for the requirements of engraving. On the other hand, Duchesne's drawings strike us by their precise layout and the attention paid to the way organs are arranged. One cannot but regret that they remained inaccessible so long.
The first author to mention their existence and their interest seems to have been Lee (1964), who published 6 of them. A short time later, the strawberry historian Darrow (1966) published 11 drawings and Wilhelm and Sagen (1974) published 5. Indeed, Darrow devoted an entire chapter to Duchesne, whereas Wilhelm and Sagen, whose main concern was the history of strawberries in the United States, only mentioned him in the course of their presentation of the different species.
The cultivator botanist and the deep naturalist
Duchesne repeatedly seems to have anticipated the criticisms which scientists were bound to address him: "It is to deep botanists that I have wished to impart my feelings, to submit them to their judgement." (p. 26); "I leave it to deep naturalists to discuss the possibility of this formation of fertile hybrids, both in animals and plants; I leave it for experimenting to determine: I will be satisfied if I have been able to prove that at least so far, no example has occurred." (p. 62).
At the time, "deep naturalists", and first of all Linné, had set it as their priority to gather the whole living world within a coherent system. That was a vast enterprise, and logically, its promoters did not wish to divide their efforts. Sachs (1892, p. 412) criticised Linnaeus in these terms: "Linné's turn of mind, his type of intelligence, and even his intellectual gifts, led him to grant experimental evidence but little value, so long as that evidence can only be experimental. From his scholastic viewpoint, he attached far greater importance to philosophical reasoning based on the idea of the plant or on reason, and he was keen on drawing analogies between plants and animais."
If this criticism helps us better understand the great difference in "turn of mind" between Linnaeus and Duchesne, it makes Linnaeus' interest in Duchesne's discoveries all the more valuable. Although experimenting was not a priority for Linnaeus, their exchanges of letters show that he was open to such approaches, a fact which was worth stressing. Nevertheless, Duchesne must have been well aware of his status in the scientific world. Indeed, he describes himself as a "cultivator botanist". When one compares this phrase with that of "deep naturalists", one cannot but relish the humour and irony hidden behind the apparent reverence of a "cultivator botanist" convinced that his approach is correct. Like many forerunners, Duchesne was right too early.
Duchesne's discoveries on strawberries are not limited to what we have been discussing. We also owe him the discovery that the five plants of Chilean strawberry (Fragaria chiloensis) introduced by Frézier were female, and could not bear fruit alone. Duchesne also confirmed the fact, already empirically known to Plougastel producers, that those Chilean strawberries could be pollinated both by the capron strawberry and by the scarlet strawberry. Finally, he was the first to express the opinion that our modern strawberry (Fragaria ananassa) was an interspecific hybrid and to point out its parents: "The Ananas strawberry is that which, among them all, I find it most difficult to place in the genealogical order... I suspect it is a result of crossings between the Scarlet strawberry and the Frutiller" (p. 197).
Duchesne is not only the strawberry man. He also played an important part in the botany of pumpkins and he drew them too. This unfamiliar aspect has recently been documented by Paris (2000a, b), but that is another matter ...
In conclusion, when one leafs through the whole collection of Duchesne's drawings, one has the impression of looking into an iconographical databank on the wild forms, cultivars and various genotypes which were known at the time. Duchesne was one of the first scientists who put together an almost exhaustive collection of living plants from a plant genus of economic interest. He described all those strawberries in detail, he studied their biology and he attempted to establish their botanical relations. This is exactly what genetic resources specialists do nowadays, with far superior scientific tools but in the same knowledge perspective. Being far from system builders, Duchesne could not but be ignored by historians of botany. Since he came much too early, he was to be ignored by historians of genetics, who start with Mendel. One can indeed be surprised at this kind of ingratitude shown by geneticists, whose subject owes its origin to the practices of gardeners and breeders far more than to scientists. But that is the way things are. If being ignored is a characteristic of forerunners, then indeed Duchesne was a great forerunner.
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