There is perhaps no better passage than Erasmus Darwin’s verse on Cassia to exemplify his philosophy of poetry and the essence of his poem, The Botanic Garden. First, the links that connect the seedpods of the Cassia plant to the biblical story of Moses and then to Britain’s abolition movement illustrate Darwin’s view of poetry as a series of images, vignettes that convey meaning all at once, rather than over time. “The Poet writes principally to the eye” (p. 48).

Second, the passage reveals the political activism at the heart of Darwin’s poem, a facet of it that is easy for the modern reader to overlook, but one that would have been readily apparent to Darwin’s contemporaries. In fact, the poem inspired multiple satires, the most clever and incisive being “The Loves of the Triangles,” which detailed the escapades of geometrical figures in jest of Darwin’s treatment of plants in his “The Loves of the Plants” (the second part of The Botanic Garden). The tripartite satire, written by three authors, appeared during April 1798 in The Anti-Jacobin. This conservative publication, inaugurated by George Canning in 1797, was, as its title implies, a reaction to the radicalism of the Jacobins, the group responsible for instituting the Reign of Terror (1793—4) during the French Revolution. In short, the journal intended to combat any elements that had the faintest whiff of French liberalism, in political, philosophic, scientific, or other guises. Darwin, who had sympathized with each of these, became a target for attack.

All of this derision, however, is yet to come when Darwin pens his seemingly desultory lines on the Cassia, a plant that presents problems of its own. Whereas Darwin provides the species for most other plants that figure in the poem, he gives only the genus, Cassia, here, leaving the reader to figure out which species he has in mind. If we consult Darwin’s translation of Linnæus, A System of Vegetables (1782), we find 30 different possible species of Cassia listed. The key to the passage, though, is that the seedpod of this particular species originates from the Americas, floats on the Gulf Stream, and makes its way to Norway’s shores. As a result, this Cassia must grow in the Americas.

Although this information narrows the list, the species determination is helped substantially more by tracking down Darwin’s own source for the passage, that is, the dissertation by the Norwegian naturalist who observed the seedpods washing up on shore. Henricus Tonning delivered the dissertation, Rariora Norvegiae, under the direction of Linnæus, in 1768. Tonning cites another, Bishop Gunner, who had catalogued all the fruits that washed up on Norway’s shores. One of these is Cassia fistula, thus revealing the species that Darwin must have had in mind. Beyond these Norwegian naturalists, Darwin, and a few others, though, it is difficult to find any references to the transatlantic passage of this plant’s seedpod. One surprising place it does turn up is in one of Henry David Thoreau’s unpublished naturalist manuscripts written after Walden. The 354-page text treats the dispersal of seeds and, sure enough, references the ability of the C. fistula to cross the Atlantic.

Darwin is interested, however, not only in the fact of this migration, but also in the means. The current that carries the seedpod from the Americas to Norway is identified as the Gulf Stream, which had caught the attention of Benjamin Franklin, who, along with Timothy Folger, created a chart of it and gave the current the name it has still to this day.

The image of the seedpod floating on the current invokes another: Moses floating on the Nile. “And when she could no longer hide him, she took for him an ark of bulrushes, and daubed it with lime and with pitch, and put the child therein; and she laid it in the flags by the river’s brink” (Exod. 2:3). In the biblical story, Moses precipitates the Exodus, freeing the Jews from Egyptian slavery. This theme of manumission, finally, allows Darwin to launch into the crescendo that ends the Canto: he pleads for abolition, a fight already well underway in Britain at the close of the eighteenth-century, at a time when the slave trade was flourishing.

Britain’s abolition movement is said to be the first political campaign, employing many of the techniques that are now taken for granted. It pioneered the use of investigative journalism, famously carried out by Thomas Clarkson, who went to the ports to interview sailors about the slave trade, later bringing the information he gathered to Parliament. Abolition’s most important parliamentary paladin was William Wilberforce, persuaded to defend the cause by Clarkson, in what may be the first instance of political lobbying. The abolition campaign also relied on judicial interventions, as in the case of the slave Jonathan Strong, on whose behalf Clarkson’s collaborator, Granville Sharp, advocated, in order to procure a landmark ruling that effectively abolished slavery in England (but not in its colonies) in 1772 by outlawing the resale of slaves to the colonies once they were in the country. Another aspect of the campaign was the publication of narratives written by slaves themselves. In 1789, Olaudah Equiano published an account of his life, describing how he and his sister had been kidnapped as children in South Nigeria and sold into slavery in Barbados and then in Virginia. The Interesting Life of Olaudah Equiano is considered to be one of the earliest books published by an African writer.

Finally, no political campaign is complete without a sound branding and merchandizing effort. This was certainly true of the abolition movement. Darwin himself references the campaign’s most iconic image, an anti-slavery cameo produced by his Lunar Society friend, Josiah Wedgwood, who is best known today for his blue and white pottery. Wedgwood’s medallion shows a slave in a supplicatory position, wrists in chains; its slogan reads, “Am I Not a Man and Brother?” The image was printed on all kinds of goods—snuff boxes, collector plates, brooches, and so on—and remains well known to this day. Its success is perhaps owing to the fact that the image has a very strategic appeal. Its creators knew their market. The slave’s position evokes the figure of a praying Christian, an important point of debate at the time. The slave is portrayed, not in rebellion, but rather as peaceful and even docile, notwithstanding the fact that freedom, often enough, was won through violent revolt. (The rebellion in Haiti was a predominant reason for Britain’s abolition of the slave trade in 1807.) Of the cameo, Darwin remarks that Wedgwood “distributed many hundreds, to excite the humane to attend to and to assist in the abolition of the detestable traffic in human creatures” (p. 87n). Darwin’s sympathies for the cause are thus stated in no uncertain terms.

What is not as clear, however, is why Darwin chose such a seemingly convoluted path to get to this impassioned plea against slavery. Would it not have been better to address one of the plants—sugarcane, coffee, cotton, tobacco, etc.—whose cultivation, harvest, manufacture, and consumption were truly at the heart of the slave trade? A point made grotesquely clear in the anonymous apology for slavery cited on this page. In general, the British were sensitive to the connection: 300,000 of them staged a boycott of slave-produced sugar in 1791. The slavery-free sugar produced in response to such boycotts and to meet the needs of socially-conscious consumers may well be the first fair-trade product. Darwin himself is by no means ignorant of the connection. In Phytologia, he recognizes the importance of sugar for animals and vegetables (as well as the dangers of its excess.) He interrupts his analyses, though, with the following: “And,—and what?—Great God of Justice! grant, that it may soon be cultivated only by the hands of freedom, and may thence give happiness to the laborer, as well as to the merchant and consumer” (p. 7). Why not, then, use sugarcane as an entrance to abolition?

As mentioned, the passage as it stands conforms well to Darwin’s ideal of poetry, and many of his other verses are also characterized by what may seem tenuous links. At the same time, his seedpod trajectory contains certain under- or unstated advantages. First, it allows Darwin to remind his readers of the Exodus, freedom from slavery in the Bible. This reminder was significant because Scripture remained a source of evidence on both sides of the abolition debate. Second, and likely more poignant rhetorically, the transatlantic migration of the seedpod recalls another forced one, the Middle Passage, which identifies the part of the triangular slave trade in which Africans were shipped to the New World. The description of its horrors played a critical role in parliamentary deliberations. In reviewing those deliberations in general up until the dissolution of the slave trade, Thomas Clarkson recounts testimonies of its miseries: suffocation from overcrowding, forced eating, despair, insanity, suicide by fasting and drowning. “And more than one,” he says, “were seen to wave their hands in triumph, ‘exulting’ (to use the words of an eye-witness) ‘that they had escaped’” (p. 223).