The value of Lindley's great work on _The Theory and Practice of Horticulture_ may be best gauged by the fact that as a statement of horticultural principles it is the best book extant. Though the botanist of the present day finds on perusing this work that physiological knowledge in 1840 was in a singularly crude state, and may rejoice at the rapid progress of discovery since the time when Lindley's book was written, yet the fact remains that few, if any, men at the present day could make a better statement of the physiological principles underlying practical horticulture than that presented by John Lindley.
Indeed it is a strange fact, and one worthy of the attention of our physiologists, that the gardeners are still endeavouring to puzzle out for themselves the reasons for their practices unaided by the physiologists. An interesting illustration of this assertion may be found in recent issues of the _Gardeners' Chronicle_ containing correspondence from many of the leading growers on the principles underlying the cultivation of the vine. No physiological Philip has come as yet to their assistance! Lindley's book had at once a great vogue on the Continent and was translated into most European languages--Russian included; but it was not till its title was changed from _The Theory_ ... to _The Theory and Practice ... of Horticulture_ that his incorrigible fellow-countrymen, as shy of theory as a fox-glove is of chalk, consented to buy it to any considerable extent.
It was doubtless due not only to Lindley's general services to horticulture but also to the special service which he rendered to that science by the publication of this work that led Lord Wrottesley, President of the Royal Society, to say, when presenting Lindley with the Royal Medal, that "he had raised horticulture from the condition of an empirical art to that of a developed science."
_"The Vegetable Kingdom" and "The Botanical Register."_
That John Lindley was a man of fine judgment is indicated by his own verdict that, except for _The Vegetable Kingdom_, _The Theory and Practice of Horticulture_ was his best book. That verdict is sustained by posterity, as Mr Botting Hemsley declares of the former work,--"This grand book must be classed as Lindley's masterpiece. No similar English work was in existence in 1846 when the first edition appeared, nor was there in any language so encyclopaedic a work. Even now it is a valuable book in a small botanical library as it is a mine of information on points that are unchangeable. The work, as set forth in the preface, originated in a desire on the part of the author to make his countrymen acquainted with the progress of Systematical Botany abroad during the previous quarter of a century." Both in his books and in his lectures he adopted the natural system of classification and did much to popularise it though, as previously stated, his contemporaries Robert Brown, the Hookers, and G. Bentham were equally powerful adherents of the new system. To quote the picturesque if somewhat immoderate language of Reichenbach "for a long time the youthful interloper found no favour on account of his having introduced in conjunction Scot Brown, Gray and the still youthful Hooker the natural system of the hated Frenchman; where the more numerous disciples of Linnæus had thought to pass their lives in the glory of pondering and admiring the great Swede." That Lindley was an early convert to this innovation is also proved by the fact that his inaugural lecture at University College startled many by its frank and thorough expression of the superficial character of the artificial system of classifying plants.