Darwin’s Botanists: Asa Gray

Holotype of Abutilon parvulum collected by Charles Wright for Asa Gray, Harvard University Herbaria.

This last post in the series (1,2,3) on Charles Darwin and the botanists who supported his work deals with an American, Asa Gray (1810-1888).  He received his medical degree at Yale University, but like Joseph Dalton Hooker (see last post), had little interest in practicing and a great desire to learn more about plants.  He taught at Utica College in central New York State for a short time, while collecting in the area and creating exsiccatae of grasses and sedges (Gray, 1834).  He was eventually drawn to work with John Torrey, a botanist who was teaching botany part time at Columbia College in New York City while also teaching chemistry at Princeton University.  Torrey was impressed with Gray’s herbarium and paid for him to collect in New York and New Jersey.  After this, Gray moved in with Torrey’s family and organized his herbarium.  This gave Gray an opportunity to see many more species than he had encountered up to this time.  He remained with the Torreys for two years until he was offered a position as professor of botany at the newly formed University of Michigan.

In preparing for this post, Gray traveled to Europe to purchase books and equipment, and also to consult much richer herbaria than those available in the US, even for American species.  Visiting Glasgow, Gray stayed with William Jackson Hooker for three weeks examining his North American plants, including many collected by Thomas Nuttall.  Gray discovered that most of the specimens were from northern areas of North America, with the south and west still relatively unexplored.  John Lindley of the Royal Horticultural Society let him take portions of the specimens said to have been collected by Thomas Walter in the Carolinas in the 1700s, something that would be unheard of today (Dupree, 1959, p. 80).  Having gathered a wealth of information, Gray returned home to find that the University of Michigan was still not ready to have him begin work.  When offered a similar position at Harvard University, with the additional responsibility for its botanical garden, he moved to Cambridge and remained there for the rest of his life. 

Gray continued to work with Torrey on the deluge of specimens coming in from US-sponsored expeditions and surveys, including the Wilkes Expedition’s 50,000 plant specimens.  This necessitated another trip to Europe to consult herbaria in Britain and France with their superior holdings of North American plants.  Torrey and Gray did much to eventually alleviate this problem by creating large collections at their home institutions of Columbia and Harvard, while the Wilkes specimens became the nucleus of the US Herbarium at the Smithsonian Institution.  Like Joseph Dalton Hooker (see last post), Torrey and Gray became “imperial” botanists, in that they attempted to retain control over collectors and discourage them from describing species themselves.  They claimed that those gathering specimens didn’t have the knowledge, reference collections, or literature to do the job. 

In 1843, US Navy Commodore Matthew C. Perry signed a treaty with Japan that began to open the country to trade.  While Perry had not wanted a natural history collector on the expedition, two Americans associated with the mission, one a friend of Gray’s, did make a small plant collection and sent it to Cambridge.  What struck Gray about these plants, as well as some other Japanese species he had encountered, was how similar they were to those of the northeast US.  When he had examined a broad enough selection, he arranged them in a table and found that of 580 Japanese species, fewer were in western North America than in Europe, and far more were in eastern North America than in either of the other areas.  Considering this odd result, he posited that the plants in these two areas had a common ancestry.  Due to fluctuating climates, which remained most similar in eastern North America and Japan, the species were better able to survive in these regions.  This was a significant piece of evidence for evolution and Charles Darwin was very pleased with it.

Gray and Darwin began their correspondence in 1855.  Darwin appreciated Gray’s acceptance of species change, though he was less pleased that Gray held that creation still had a role in life on earth.  Gray presented this view most fully in an article in the Atlantic Monthly in 1861, “Natural Selection Not Inconsistent with Natural Theology.”  While disagreeing with it, Darwin did see it as a way to lure more people into the evolutionary fold and arranged for it to be reprinted in Britain (Dupree, 1959, p. 155).  Like Hooker, Gray also provided Darwin with much botanical information for his post-Origin plant studies.  They both experimented in their gardens, and Gray could provide seeds and cuttings of American plants.  In his own work, Gray was stymied by the amount of administrative work he was required to do at Harvard without adequate assistance.  Until he retired, he was the only professor of botany, and the University had never created an infrastructure for botanical research.  Gray managed to set the stage for this at his retirement by donating his herbarium of 220,000 specimens and his library of over 2,200 books to the University and managing the hiring of a staff to at last create a department of botany.   


Dupree, A. H. (1959). Asa Gray: American Botanist, Friend of Darwin. Cambridge, MA: Harvard University Press.

Gray, A. (1834). North American Gramineae and Cyperaceae (Vols. 1–2). New York, NY: Post.

Darwin’s Botanists: Joseph Dalton Hooker

Illustration of Rhododendron glaucum from Joseph Hooker’s The Rhododendrons of Sikkim-Himalaya, Biodiversity Heritage Library.

Joseph Dalton Hooker (1817-1911) was born into the botanical world.  His father was William Jackson Hooker (1785-1865), a botany professor at the University of Glasgow who then became director of the Royal Botanic Gardens, Kew.  Joseph eventually succeeded his father in that post, but his career had more bumps than this succession might suggest.  The Hookers did not have the wealth of the Darwins, so they needed salaried appointments in order to pursue their interest in science, something Charles Darwin never had to consider.  William could provide for his family, but as an adult, Joseph had to find his own means of support after graduating with a medical degree from the University of Glasgow.  Eight years younger than Darwin, Joseph Hooker took a similar route to gain experience in natural history by participating in the British Navy’s Ross Expedition to Antarctica, serving as assistant surgeon; both he and the surgeon were also charged with collecting natural history materials.  Setting out in 1839, they visited South Africa and several groups of islands on their way to and from Antarctica, as well as Australia, New Zealand, and Tierra del Fuego. 

By the time Hooker arrived back in Britain four years later, he had not only amassed a large herbarium but also made many drawings.  Like his father he was an accomplished botanical artist and created many of his own illustrations, especially for his early publications.  On his return to Britain, he began work on studying his collection and publishing descriptions of new species.  Hooker also analyzed some of Darwin’s specimens from the Beagle expedition.  Eventually Hooker described many of them and in the process became quite friendly with Darwin who was thrilled to have his plant collection studied after the long delay in John Henslow’s hands (see last post).  Their friendship flourished and continued until Darwin’s death.

In 1841 William Hooker became director of Royal Botanic Gardens, Kew, but there was no paid position available to his son.  Joseph applied to be professor of botany at Edinburgh, but didn’t get the job, so he worked for the British Geological Survey and learned paleobotany.  In 1847, he went on another expedition, this time to the Himalayas as a plant collector financed by Kew.  He sketched many of the plants, especially the rhododendrons, and it is amazing how beautiful these sketches are considering the rough conditions under which he worked (see above).  When Joseph returned to Britain he went to work on his collections, and finally obtained a paid position at Kew as his father’s assistant in 1855.  Ten years later, when his father died, he became director and was paid to cede the elder Hooker’s herbarium to Kew where he could still have access to it. 

In the meantime, Darwin had been developing his ideas on evolution, having written up a 230 page “summary” in 1844.  He had copies made and gave them, in sealed envelopes, to his wife Emma and to Joseph Hooker so that in case of his death it could be published, though he wasn’t ready to do the deed himself.  At one point after this, Hooker bluntly suggested that while Darwin’s interests were definitely broad, extending from variation in domesticated animals to fossils to plant breeding, he really hadn’t delved deeply into any one group of organisms.  He needed to study some segment of the living world so closely that he would get a sense of the issues involved in distinguishing one species from another.  This was the start of Darwin’s eight-year odyssey studying barnacles that resulted in a two-volume publication on them.  Janet Browne (1995) sees this as Hooker’s most significant contribution to Darwin’s thinking. 

Hooker was also very involved in dealing with the crisis that overwhelmed Darwin when he received a letter from Alfred Russel Wallace in 1858 outlining a theory of natural selection very similar to Darwin’s own.  Hooker and the geologist Charles Lyell calmed Darwin down and devised a plan in which they presented Wallace’s paper, along with a short summary of Darwin’s work, at a meeting of the Linnean Society of London (Browne, 2002).  This was another major event in Hooker’s relationship with Darwin and led to Darwin’s writing On the Origin of Species (1859) within a year.  Though they didn’t always agree on all the finer points of the theory, Hooker remained an important support to Darwin especially because in the years after publication of The Origin, Darwin wrote a number of major works on plants.  Hooker supplied not only advice and taxonomic assistance, but also sent Darwin orchids and other plants from Kew. 

Hooker had an illustrious career in his own right as described in Ray Desmond’s biography (1999).  In Imperial Botany, John Endersby (2008) takes a different tack toward Hooker’s profession and analyzes how he used his position at Kew to command an army of collectors around the world to add to the already outstanding herbarium his father had amassed.  Endersby argues that Hooker was intent on remaining in control of plant taxonomy, particularly of naming new species.  He sternly directed collectors to send the material to Kew rather than attempt to describe species themselves.  Such tight reins were difficult to maintain as collectors became more knowledgeable about the plants where they lived and collected, for example, in Australia and India.  Hooker’s argument was that they lacked the broad collection he had available and so tended to see something as a new species, when it was only a variant (Boulter, 2009).  In other words, colonial botanists were splitters and imperial botanists like Hooker were lumpers.  During his career, Hooker published an impressive array of books including Genera Plantarumwith George Bentham, The Rhododendrons of Sikkim-Himalaya, and Flora of British India, as well as works on plants he collected in Tasmania, New Zealand, and Antarctica. 


Boulter, M. (2009). Darwin’s Garden: Down House and the Origin of Species. Berkeley, CA: Counterpoint.

Browne, J. (1995). Charles Darwin: Voyaging. Princeton, NJ: Princeton University Press.

Browne, J. (2002). Charles Darwin: The power of place. Princeton, NJ: Princeton University Press.

Desmond, R. (1999). Sir Joseph Dalton Hooker: Traveller and Plant Collector. Kew, UK: Royal Botanic Gardens, Kew.

Endersby, J. (2008). Imperial Nature: Joseph Hooker and the Practices of Victorian Science. Chicago: University of Chicago Press.

Darwin’s Botanists: John Stevens Henslow

Specimens of Phleum arenarium in the John Henslow Herbarium, Cambridge University.

John Stevens Henslow is perhaps best known today as Charles Darwin’s botany teacher at Cambridge University and as the person who presented Darwin with an invitation to join the Beagle surveying expedition headed by Captain Robert FitzRoy.  However, this leaves out the herbarium part of the story, obviously the good part.  It’s not surprising that Henslow had an herbarium, but the way he handled his specimens was a little different.  In an article called “What Henslow Taught Darwin,” a team of researchers found that two-thirds of Henslow’s sheets at the Cambridge University Herbarium are what he termed “collated,” that is, having more than one specimen (Kohn et al., 2005).  This doesn’t seem noteworthy, especially for small plants, but their placement is interesting.  They were sometimes arranged in order of increasing height (see above), or with the largest specimen in the middle and specimens in descending height order on either side.  In many cases, specimens on a sheet included ones with different collectors, dates, and locations. 

Many of the specimens were collected around the time Henslow was teaching Darwin and also working on variation within plant species.  He grew Primulas, varying the amount of moisture, manure, and shade, noting that they differed in ways often seen in the field.  Earlier, he had made drawings of the different lengths of styles and stamens in cowslips, Primula veris, something Darwin later investigated.  Kohn and his coauthors argue that the specimens and observations on variation that Henslow presented in his lectures became part of Darwin’s “mental architecture,” so much a part of his thinking that he might not have even realized the debt he owed to Henslow.  This wasn’t just from the three cycles of Henslow lectures that Darwin attended.  Janet Browne (1995) notes that they became closest during Darwin’s last months at Cambridge when they often went on walks and collecting trips, and dined together at Henslow’s house.  It was then that Henslow arranged for his student to accompany Adam Sedgewick, Cambridge’s professor of geology, on a field trip to Wales.  This cemented Darwin’s interest in geology, which was important to his observations on the Beagle.  It was also when Darwin’s oldest known herbarium specimens were collected, three Matthiola sinuata, that were collated by Henslow on a single sheet along with another example collected by a Miss Blake.    

Darwin had an opportunity to collect many plants on the Beagle expedition, hundreds of them, which he sent to Henslow along with animal skins, fossils, etc.  After shipping the first package, he had to wait two years for a letter from Henslow to catch up with him.  In the meantime, he worried that no correspondence meant that Henslow wasn’t pleased with what he sent.  He was relieved to finally read that Henslow was grateful for the materials.  However, his mentor did comment that Darwin shouldn’t send scraps, that the entire plant should be included when possible—leaves, roots, stem, flowers—and that one of the leaves should be turned back to reveal the underside.  Also, it wasn’t necessary to sew down the specimens; they traveled better when left loose (Allan, 1977). 

Soon after his return to England, Darwin delivered the last batch of specimens in person, and Henslow agreed to begin work on identifying them.  However, this turned out to be a slow process, in part because the assignment coincided with Henslow’s move from Cambridge to become vicar at a church in Hitcham, almost 50 miles away.  He remained a Cambridge professor, but usually only visited there to give his lectures.  Another problem was that so many of the plants were unfamiliar to Henslow.  Darwin kept prodding him for several years, until eventually Henslow turned the specimens over to the young botanist Joseph Dalton Hooker, who had himself just returned from a round-the-world expedition with the British Navy.  Hooker found that many of the plants that Darwin collected on the Galapagos Islands were endemic to the islands, and in many cases, occurred on only one Island, information that Darwin was relieved to hear since it fit with his observations on birds and other animals.

Henslow might not have had time for Darwin’s plants, but he made a number of other contributions to botany (Walters & Stowe, 2001).  He revitalized the botany program at Cambridge University.  It had become rather dormant under the nearly 60-year reign of Thomas Martyn, who spent much of his time as a London physician.  He overhauled the herbarium, which had become disorganized.  Henslow made it known that he was building the collection, particularly with plants from Cambridgeshire and Great Britain, and received notable donations.  He pressed for a new, larger botanic garden at the university to replace the one that had fallen into disrepair and then oversaw this project.  Henslow’s lectures were well-received, and they were accompanied with specimens and with charts he drew.  He wrote and illustrated a text to go with his course, and later, with help from his daughter and the noted artist and engraver Fitch, published a series of large botanical charts for sale to schools (Burk, 2005).  Henslow wrote papers on plant variation and on zoological aspects of natural history, most before his move away from Cambridge.  In all, he produced significant contributions to botanical science besides serving as Darwin’s mentor and travel arranger. 


Allan, M. (1977). Darwin and His Flowers: The Key to Natural Selection. New York, NY: Taplinger.

Browne, J. (1995). Charles Darwin: Voyaging. Princeton, NJ: Princeton University Press.

Burk, W. (2005). Henslow’s wall charts: A legacy of botanical instruction. Bulletin of the Hunt Institute for Botanical Documentation, 17(1), 4–6.

Kohn, D., Murrell, G., Parker, J., & Whitehorn, M. (2005). What Henslow taught Darwin. Nature, 436, 643–645.

Walters, S. M., & Stow, E. A. (2001). Darwin’s Mentor: John Stevens Henslow, 1796-1861. Cambridge, UK: Cambridge University Press.

Darwin’s Botanists: In the Family

Frontispiece for Eramus Darwin’s The Botanic Garden, Biodiversity Heritage Library

In this series of post’s I’ll be discussing key botanists who influenced Charles Darwin’s work:  John Stevens Henslow, Joseph Dalton Hooker, and Asa Gray.  But first I’ll look at those closer to home who were important to Darwin’s development as a naturalist.  The most obvious is his grandfather, Erasmus Darwin, a physician with broad interests including botany.  He worked with two others in his town of Litchfield to translate some of Linnaeus’s work, and after that wrote a volume of poetry, The Love of Plants, as an introduction to the Linnaean classification system.  It was well-received and was followed by The Economy of Vegetation; the two were then published together as The Botanic Garden.  There are hints of evolutionary thinking in them, but are more overt in Zoonomia, a two-volume medical work with a chapter on generation that presents a somewhat Lamarckian view of species change.  Erasmus died before Charles Darwin was born, so most of his grandfather’s influence on him was through his writings.  By the time Charles was studying at Cambridge, he was aware of Erasmus’s ideas as well as those of Lamarck.

Darwin’s father Robert was also a physician interested in botany, though not a writer.  However, he took pleasure in gardening with his children.  This is probably how Charles was first introduced to nature, and he early had a fascination with plants and animals, with closely observing nature as every good gardener must.  Since it’s impossible to garden without encountering insects, it was probably in working with his father that Charles developed his interest in insects and became a collector.  Robert also kept a notebook where he recorded phenological events such as first flowerings, something that his son and grandsons also did.  At one point Robert set the young Charles the task of counting the number of peony blooms each year.  What I find interesting about this is that the number varied from 160 to 363, an impressive display.

Robert Darwin hoped that Charles would follow in his father’s and grandfather’s footsteps, not only in gardening but in becoming a physician as Robert’s older son, Erasmus, did.  But after spending two years at the University of Edinburgh studying medicine, Charles had to break it to his father that he was not cut out to be a physician (Browne, 1995).  It was a tremendous relief to be free of that burden, and Robert sent his son off to Cambridge to become a clergyman, a profession that was at the time full of naturalists.  At Cambridge Darwin met the cleric/professor of botany, John Stevens Henslow, but that is the story of the next post.

While at the university, Darwin became friendly with a cousin, William Darwin Fox, who was also interested in natural history, particularly entomology.  It was Fox who introduced Darwin to the wonders of beetles.  This was a time when divisions between biological disciplines was permeable so in hunting for beetles it was impossible not to take an interest in birds, plants, and even aquatic life that filled the wetlands around Cambridge.  After acquiring a microscope from a friend, Darwin became fascinated by the world of aquatic invertebrates and studied their reproductive cycles.  There seemed to be no aspect of natural history that didn’t engage him.  At the end of his time at Cambridge, he went on a geological fieldtrip to Wales with Adam Sedgewick, professor of geology, and there he made what is considered his oldest existing herbarium sheet. 

After Cambridge came Darwin’s five years of travel on the Beagle which involved collecting specimens that he sent back to Henslow.  In fact, Henslow served as receiver for all eight shipments of plants, animals, fossils, and rocks that Darwin had amassed.  I’m skipping forward very rapidly, but much of this story is familiar to many of you, and for those who want more detail, Janet Browne’s two-volume biography is a joy to read (1995, 2002).  As he was creating the first draft of his theory of species change in 1838, Darwin decided to marry Emma Wedgewood.  They had 10 children, seven of whom lived to adulthood, and all were assistants in his work to a greater or lesser extent.  They pitched in with the endless experiments Darwin devised at Down House, their home in the country outside London.  As they got older, they took on more responsibility.  His daughter Henrietta was his editor and proofreader, and his sons George and William made many of the drawings for his botanical works.  Darwin even engaged George Sowerby, a member of a distinguished family of natural history artists, to teach engraving to George Darwin, whose daughter became the famous printmaker Gwen Raverat.  She also wrote a great book on growing up a Darwin in Cambridge (1952).

Francis Darwin was the son who was most involved in Darwin’s later scientific work, particularly in investigating plant movements and phototropism.  Francis’s first wife died in childbirth.  To ease his grief, his parents urged him to move back to Down House with his infant son.  This is when his collaboration with his father became particularly close, and they co-authored The Power of Movement in Plants, published in 1880, two years before Charles’s death.  Francis also edited collections of his father’s letters.  So even without going outside his family, Darwin received a great deal of inspiration and assistance from those related to him, across the generations.  In the following posts, I’ll discuss some of those outside the family who were also important to his botanical work.


Browne, J. (1995). Charles Darwin: Voyaging. Princeton, NJ: Princeton University Press.

Browne, J. (2002). Charles Darwin: The power of place. Princeton, NJ: Princeton University Press.

Raverat, G. (1952). Period Piece: A Cambridge Childhood. London: Faber & Faber.