Sufficient has now been said to indicate that Hooker's work was that of a pioneer, in providing the material foundation necessary for the further study of the science, not only in this country, but also in the furthest lands of the Empire. He supplied a coordinating centre for botanical organisation in Britain, and for that service he has earned the lasting gratitude of botanists. It remains to review his own published works, and base upon them some estimate of his more direct influence upon the progress of the science. We shall see that in this also his work was largely of that nature which affords a basis for future development. It was carried out almost entirely under pre-Darwinian conditions. He was pre-eminently a descriptive botanist, who worked under the influence of the current belief in the constancy of species. But his enormous output of accurate description and of delineation of the most varied forms, has provided a sure basis upon which the more modern seeker after phyletic lines may proceed.
There have been few if any writers on botanical subjects so prolific as Sir William Hooker, and probably none have ever equalled him in the number and accuracy of the plates which illustrated his writings. Sir Joseph Hooker estimates the number of the latter at nearly 8000, of which about 1800 were from drawings executed by himself. The remainder were chiefly from the hand of Walter Fitch, who acted as botanical limner to Sir William for thirty years, showing in the work fidelity, artistic skill and extraordinary rapidity of execution. The numbers quoted give some idea of the magnitude of the results.
For the purpose of a rapid review of the chief writings of Sir William's later years, they may be classified under three heads, viz. (1) Journals, (2) Floristic works, and (3) Writings on the Filicales. Taking first the Journals, one of the most remarkable features about them is the apparent variety and number of the enterprises on which Sir William engaged: this is, however, explained when they are pieced together as they will be found below. His connection during 45 years with large and growing gardens, into which the most varied living specimens were being drafted in a constant stream, put him in possession of a vast mass of facts, detached, but needing to be recorded. The materials were thus present for that type of publication styled a Botanical Miscellany. The majority of the serials which he edited took this form, and though published under various titles, dictated in some measure by the source of their publication, more than one of them was a mere continuation of a predecessor under a different title. The first of them appeared under the name of the Exotic Flora, in three volumes (1823-7), with 232 coloured plates illustrating subjects from the Gardens of Glasgow, Edinburgh, and Liverpool. But owing to his taking up in 1827 the editorship of the Botanical Magazine, then in a critical position, the Exotic Flora ceased, and its materials swelled the pages of the more ancient serial, with which he was connected till his death.
To those not intimately acquainted with the other serials edited by Sir William, their relations are difficult to trace. But Sir Joseph Hooker has given their titles in series, with their dates, as follows:
Botanical Miscellany. 3 vols. 1830-33.
Journal of Botany. 1 vol. 1834.
Companion of the Botanical Magazine. 2 vols. 1835-36.
Jardine's Annals of Natural History. 4 vols. 1838-40.
The Journal of Botany (continued). Vols. ii.-iv. 1840-42.
The London Journal of Botany. 7 vols. 1842-48.
The Companion of the Botanical Magazine. (New Series. 1845-48.)
London Journal of Botany and Kew Gardens Miscellany. 9 vols. 1849-57.
From this list it appears that throughout a long term of years, though under varying titles, the stream of information gathered chiefly through garden management was edited and published, taking the form of 28 volumes, with 556 plates.
The "Floristic" works of Sir William Hooker began with the second edition of Curtis's Flora Londinensis, in five folio volumes, upon which he worked from 1817 to 1828. He contributed a large proportion of the plates from his own drawings, while the descriptions throughout (excepting those of the plates on Algae and Fungi by R. K. Greville) were enlarged, and rewritten by him. He was in fact the real author of the work, which, however, was so badly edited—even the letter-press was not paged—that citation of it was impossible, and it never took its proper place as a scientific work. Sir Joseph Hooker points out that the second edition was not properly styled Flora Londinensis, since it included many species which are not indigenous anywhere near London. But these were the lapses of the editor, not of the author and artist. Minor works were the accounts of the plants collected on Parry's and Sabine's Arctic voyages (1823-28), but the Flora Boreali Americana was a more important undertaking. It appeared as two quarto volumes (1829-40), in which 2500 species were described with numerous illustrations. It was based on the collections of various travellers, and included ferns and their allies. In 1830 came the first edition of the British Flora, a work which was continued through eight editions, the last being in 1860, and it contained 1636 species. The botanical results of Beechey's voyage in the "Blossom" to the Behring Sea, the Pacific Ocean, and China were produced jointly with Dr Walker-Arnott in 1830-41, as a quarto volume, with descriptions of about 2700 species, and notable for the diversity of the floras included. In 1849 the Niger Flora appeared, dealing with the collections of Vogel on the Niger expedition of 1841. But the most remarkable of all these floristic works was the great series of the Icones Plantarum. It was initiated in 1837 for the illustration of New and rare plants selected from the Author's Herbarium, and was continued by him till his death in 1865. Owing to the munificence of Bentham's bequest to the Kew Herbarium for its continuance and illustration, it remains still as the principal channel for the description and delineation of new and rare plants from the Kew Herbarium. The fact that the number of the plates is now about 3000 gives some idea of the magnitude of this work, which was started by Sir William Hooker in the later days of his Glasgow professorship.
It might well be thought that the production of the works already named would have sufficed to occupy a life-time, especially when it is remembered that they were produced in the intervals of leisure after the performance of the official duties of a professor, and later of the Director of the growing establishment at Kew. But there still remain to be mentioned that noble series of publications on the Filicales, which gave Sir William Hooker the position of the leading Pteridologist of his time. The series on ferns began with the Icones Filicum (1828-31) in two folio volumes, with 240 coloured plates by R. K. Greville, the text being written by Hooker. The same authors again cooperated in the Enumeratio Filicum (1832), a work projected to give the synonymy, citation of authors, habitat, and description of new and imperfectly known species. But it only extended to the first 13 genera, including the Lycopodineae, Ophioglosseae, Marattiaceae, and Osmundaceae, and was then dropped. Here may be conveniently introduced a number of volumes, which were for the illustration of ferns, but not systematically arranged. They were issued from time to time, and collectively give a large but not a coordinated body of fact. They were, the First Century of Ferns, issued in 1854; the Filices Exoticae in 1859; a Second Century of Ferns in 1861; British Ferns also in 1861, and Garden Ferns in 1862.
There still remain to be mentioned three great systematic works on ferns, each of which is complete in itself, viz. the Genera Filicum, the Species Filicum, and the Synopsis Filicum. The first of these was the Genera Filicum (1838-40), a volume issued in parts, royal octavo, with 126 coloured plates illustrating 135 genera. It goes under the joint names of Francis Bauer and Sir William Hooker, the latter being described on the title-page as Director of Kew. But the preface is dated May 1, 1838, from Glasgow, and it was printed at the University Press. The title-page further states that the plates were from the drawings of F. Bauer, but Sir Joseph Hooker points out (l.c. p. cviii), that "of the whole 135 genera depicted I think that 78 are by Fitch." Sir William in the preface states that "The plates have all been executed in my own residence, and under my own eye, in zincography, by a young artist, Walter Fitch, with a delicacy and accuracy which I trust will not discredit the figures from which they were copied." The result is one of the most sumptuous volumes in illustration of a single family ever published. After 70 years it is still the natural companion of all Pteridologists. At its close is a synopsis of the genera of ferns, according to Presl's arrangement, which Sir William describes as "the most full and complete that has yet been published." But in the preface he remarks that Presl "has laid too much stress on the number and other circumstances connected with the bundles of vessels in the stipes, which in the Herbarium are difficult of investigation." This is a specially illuminating passage for us at a time when anatomical characters are becoming ever more important as phyletic indices. It shows that readiness of diagnosis was for him a more important factor than details of structural similarity.
In the preface to the Genera Filicum Sir William says, he "would not have it to be understood that the Genera here introduced are what I definitely recommend as, in every instance, worthy of being retained.... A more accurate examination of the several species of each Genus, which are now under review in the preparation of a Species Filicum, will enable me hereafter to form a more correct judgement on this head than it is now in my power to do." The five volumes of the Species Filicum thus promised, appeared at intervals from 1846 to 1864. The work is briefly characterised by Sir Joseph as consisting of "descriptions of the known Ferns, particularly of such as exist in the Author's Herbarium, or are with sufficient accuracy described in the works to which he has had access, accompanied by numerous Figures. This which will probably prove to be the most enduring monument to my father's labour as a systematist and descriptive pteridologist, is comprised in five 8vo volumes, embracing nearly 2500 species, with 304 plates by Fitch, illustrating 520 of these. It occupied much of the latter eighteen years of his life, the last part appearing in 1864." The work is a most extraordinary mine of detailed information. It is a condensed extract from his own unrivalled Herbarium of Ferns, with exact data of distribution, and collectors' numbers. Probably no family so extensive as this has ever been monographed by a single hand with such minuteness and exhaustive care. It is the classic book of reference in the systematic study of ferns. But as indicated in the preface to the Genera, the judgement as to which genera are "worthy of being retained" had been exercised. The result was the merging of a number of the genera of Presl, and others, into neighbouring genera. Though this was somewhat drastically done in the Species Filicum, it comes out more prominently in the work upon which he entered in the very last months of his life, viz. the Synopsis Filicum. This work was published in 1868 as an octavo volume, with 9 coloured plates, containing analyses of 75 genera. Sir Joseph tells us (l.c. p. 117) that "Upon this work my father was engaged up to a few days before his decease, and 48 pages of it in print were left on his desk, together with the preface and much matter in manuscript. After full consideration it appeared to me that, with the material in hand, the aid of the Species Filicum completed only three years earlier, and of the Fern Herbarium in perfect order, and named according to his views, a competent botanist should find no great difficulty in carrying on this work to its completion. Such a botanist I knew my friend Mr Baker to be, and also that he had made a study of Ferns, and accepted my father's limitations of their genera and species. I therefore requested that gentleman to undertake the work, which to my great satisfaction he has done. The Synopsis Filicum contains 75 genera, and about 2252 species, inclusive of Osmundaceae, Schizaeaceae, Marattiaceae, and Ophioglossaceae, which are not included in the Species Filicum." This work summarised the Pteridological results of Sir William Hooker's life. The total number of plates of ferns published by him is about 1210, embracing 1267 species, of which about 250 appeared under the joint authorship of Dr Greville and himself. These figures are in themselves sufficient evidence of the extent of his Pteridographic work.