The third and last edition of _The Vegetable Kingdom_ consists of about 1000 pages in small type with upwards of 500 illustrations. It contains an historical review of the various "Natural Systems" which had been prepared, beginning with John Ray's (1703) and ending with his own, which is used in the work. In this system Lindley divided plants into seven classes:--Thallogens, Acrogens, Rhizogens, Endogens, Dictyogens, Gymnogens and Exogens, and each class was subdivided into alliances or groups of Natural Orders to which he gave names of uniform termination, as Algales, Filicales, Glumales, Malvales, etc. This classification, though ingenious, is defective, as the author himself recognised. Though never adopted by other writers this fact did not prevent Bentham and Hooker from citing Lindley's work frequently in their _Genera Plantarum_. As Mr Botting Hemsley observes, Lindley, who in all questions of classification was both cautious and modest, seems to have been an evolutionist without knowing it. Thus in the course of discussion on the permanency of species he observes that "all the groups into which plants are thrown are in one sense artificial, in as much as nature recognises no such groups. As the Classes, Natural Orders and Genera of botanists have no real existence in Nature, it follows that they have no fixed limits and consequently it is impossible to define them.... An arrangement then which shall be so absolutely correct an expression of the plan of nature as to justify its being called _the_ Natural System is a chimera."
Owing to the fact that Hooker wrote the admirable and favourable review of the _Origin of Species_ which appeared in the _Gardeners' Chronicle_, it has been inferred that Lindley himself was not very well disposed toward the new theories; but Lord Lindley states that his father was much impressed by the _Origin_, said it would revolutionise botanical studies but that there were difficulties which would require elucidation before Darwin's theory could be regarded as completely satisfactory--surely a perspicacious judgment.
To turn to the woodcuts of _The Vegetable Kingdom_ affords both pleasure and relief--pleasure on account of their excellence, relief to escape from the monotonous prettiness of modern process work.