Naturally so ardent a botanist desired to widen his experience by travel. But circumstances checked the projects which he successively formed to visit Ceylon and Java, South Africa, and Brazil. In 1814 he went to France, and became acquainted with the leading botanists of Paris. He proceeded to Switzerland and Lombardy, returning in 1815, in which year he married the eldest daughter of his friend Mr Dawson Turner. Meanwhile, at his father-in-law's suggestion he had embarked in a business for which he was not specially fitted by experience or by inclination. It did not prove a success, and as the years drew on, having a young family dependent upon him, he began to look out for some botanical appointment which should at once satisfy his personal tastes, and be remunerative. The chair in Glasgow becoming vacant in 1820 by the transfer of Dr Graham to Edinburgh, he received the appointment from the Crown, largely through the influence of Sir Joseph Banks. He entered upon its duties never having lectured before to a class of students, nor even heard such lectures, but otherwise equipped for their performance in a way that would bear comparison with any of the professors of his time.
Glasgow was in 1820 at an interesting juncture in its botanical history. Though the science of botany had been taught for a whole century in the University, a separate chair had been founded by the Crown only two years before. Moreover, though there had been for a long period a "Physic Garden" in the grounds of the old College, this had proved insufficient, and its position within the growing town unsuitable. Accordingly, in part by grant from the Crown, partly from the funds of the University, but largely by the subscriptions of enthusiastic citizens a Botanic Garden had been founded under Royal Charter in 1817, and opened to the public in 1819. The first blush of novelty had not worn off this new enterprise when a man, already in a leading position, whose successful achievements had shown his quality, acquainted with many of the leading botanists of Europe, and with youth and unbounded energy at his disposal entered upon the scene, and began that course of organisation of Public Botanic Gardens which he continued to the day of his death.
There was nothing to prevent the Glasgow establishment from rapidly taking a leading position. Largely as the result of Hooker's influence and initiative, and assisted greatly no doubt by the zeal with which the movement was supported by individual citizens, and aided by the position of Glasgow as a great commercial centre, contributions to the garden began to come in from every quarter of the globe. Taking the number of species represented as a measure, the growth of the living collections was rapid beyond precedent. In 1821 the number of species living in the garden was about 9000: in 1825 it is quoted at 12,000, while the increase in number from that period onwards was about 300 to 500 per annum. Of these a large number were new species, not previously described or figured. This work Hooker carried out, and the publication of his results widened still further the desire of the officials of other gardens to effect exchanges. In 1828, after it had been in existence but ten years, the Glasgow garden was corresponding as an equal with 12 British and Irish, 21 European, and 5 Tropical gardens, while it had established relations with upwards of 300 private gardens. In 1825 Sir William Hooker published a list of the living plants in pamphlet form, with a plan of the garden, copies of which are still extant. But the following years, from 1825 to 1840 were the most notable in its history as a scientific institution. It is recorded in the minute books that scientific visitors almost invariably expressed the opinion that the garden would not suffer by comparison with any other similar establishment in Europe. It can hardly have come as a surprise to those who had witnessed his work in Glasgow that when a Director had to be appointed to the Royal Gardens at Kew, the post was offered to Hooker. He accepted the appointment and left Glasgow in 1841.
His conduct of the Glasgow professorship from 1820 to 1841 was a success from the first, notwithstanding his entire want of prior experience of such duties. Sir Joseph Hooker, in his speech at the opening of the New Botanical Buildings in Glasgow University, in 1901 pointed out how he "had resources that enabled him to overcome all obstacles: familiarity with his subject, devotion to its study, energy, eloquence, a commanding presence, with urbanity of manners, and above all the art of making the student love the science he taught." Not only students in medicine, for whom the course was primarily designed, attended the lectures, but private citizens, and even officers from the barracks.
Sir Joseph describes his father's course as opening with a few introductory lectures on the history of botany, and the general character of plant-life. As a rule the first half of each hour was occupied with lecturing on organography, morphology, and classification, and the second half with the analysis in the class-room of specimens supplied to the pupils, the most studious of whom took these home for further examination. An interesting event in these half-hours was the professor calling upon such students as volunteered for being examined, to demonstrate the structure of a plant or fruit placed in the hands of the whole class for this purpose. The lectures were illustrated by blackboard drawings, probably these were a special feature in the hands of so experienced an artist as he, and also by large coloured drawings, chiefly of medicinal plants, which were hung on the walls. Another feature, which happily still survives, was the collection of lithographed illustrations of the organs of plants, a copy of which was placed before every two students. The first edition of these drawings appears to have been by his own hand. But in 1837 a thin quarto volume of Botanical Illustrations was produced, "being a series of above a thousand figures, selected from the best sources, designed to explain the terms employed in a course of Lectures on Botany." The plates were executed by Walter Fitch, who was originally a pattern-drawer in a calico-printing establishment, and entered the service of Sir William in 1834. This great botanical artist continued to assist Sir William till the death of the latter, and himself died at Kew in 1892. A number of copies of this early work of Fitch remain to the present day in the Botanical Department in Glasgow.
Other branches, however, besides Descriptive Organography were taken up. Naturally the plants of medicinal value figured largely in the course, which was primarily for medical students. Illustrative specimens, of which Sir William gathered a large collection, were handed round for inspection. These, together with other objects of economic interest finally made their way to Kew, and were embodied in the great collections of the Kew Museums. The branch of anatomy of the plant-tissues was not neglected. Of this he wrote at the time of taking up the duties of the chair, "it is a subject to which I have never attended, and authors are so much at variance as to their opinions, and on the facts too, that I really do not know whom to follow." He continues with a remark which is singularly like what one might have heard in the early seventies, just before the revival of the laboratory study of plants in this country. He remarked that "Mirbel has seen what nobody else can: so nobody contradicts him, though many won't believe him." I can hardly doubt that physiology of plants will also have figured in the course, first because Sir William was himself a successful gardener, but secondly because we have in the Botanical Department in Glasgow the syllabus of the lectures of Professor Hamilton who taught botany in the University in the latter end of the 18th century. In this course physiology took a surprisingly large place, and we can hardly believe that it would have dropped out of Sir William's course altogether. But of this there is no definite record.
Another feature of the teaching of Sir William was the practical illustration of botany in the field, by means of excursions. Of these Sir Joseph tells us there were habitually three in each summer session, two of them on Saturdays, to favourable points in the neighbourhood of Glasgow; but the third, which took place about the end of June, was a larger undertaking. With a party of some thirty students, and occasional scientific visitors from elsewhere, he started for the Western Highlands, usually the Breadalbane range. In those days, before railways, and often with indifferent roads, this was no light affair, and in some cases it involved camping. I do not know whether this was the beginning of those class excursions which have been so marked a feature in the botanical work of the Scottish Universities, but it is to be remembered that his immediate successor in the Glasgow chair was Dr Hutton Balfour, who in later years confirmed and extended the practice, and it has been kept up continuously in the Scottish universities ever since. It was to meet the requirements of such work in the field that Sir William prepared and published the Flora Scotica. The first edition appeared before his second year's class had assembled in 1821. The first Part related to the Phanerogams only, arranged according to the Linnaean system. The second, which seems to have been almost as much a new book as a second edition, contained the Phanerogams arranged according to the natural system, just then coming into general use. It also embodied the Cryptogams, in the working up of which he had the assistance of Lindley and of Greville. The total number of species described was 1784, of which 902 were Cryptogams.
And thus was initiated that profuse and rapid course of publication which characterised the period of office of Sir William Hooker in Glasgow. The duties of the chair were comparatively light, and only in his later years did he extend them voluntarily into the winter months. He worked year in year out, early and late, at his writing, and rarely left home. The 21 years of his professorship were perhaps the most prolific period of his literary production. It was brought to a close in 1841, by his appointment to the directorship of the Royal Gardens at Kew, which had in March 1840 been transferred from the Crown, under the Lord Steward's Department, to the Commissioners of Woods and Forests. Sir William had been for some time desirous of changing the scene of his activities from the relatively remote city of Glasgow to some more central point, and the opening at Kew not only satisfied this wish, but also put him in command of the establishment in which he saw, even in its then undeveloped state, the possibility of expansion into a botanical centre worthy of the nation.
In the spring of 1841 Sir William removed to Kew, taking with him his library, his private museum and herbarium. This was the first of those incidents of denudation of the botanical department in Glasgow, the direct result of the system that held its place in the Scottish Universities till the Act of 1889. Till that date the chair was "farmed" by the professor. Almost all the illustrative collections and books of reference were his private property. Whenever, as has repeatedly been the case in Glasgow, the occupant of the chair was promoted elsewhere, he naturally took his property with him, and the University was denuded, almost to blank walls. Fortunately that is so no longer. But in the present case the collections were removed, and finally formed the basis of the great museums, and of the herbarium of Kew.