The general scheme of classification, which Dodoens propounded, has much in common with that of d’Aléchamps, which we have already outlined. Within the larger groups, he shows a stronger perception of natural grouping than appears in his arrangement of the larger classes themselves. He often grouped together genera which we now regard as members of the same natural order, and species which we now look upon as belonging to a single genus. For instance he brought together genera belonging respectively to the Geraniaceæ, Hypericaceæ, Plantaginaceæ, Cruciferæ, Compositæ, etc. In some cases, however, he was only partially successful, as in the Umbelliferæ, among which he described Nigella (Love-in-a-Mist) and a couple of Saxifrages. This example shows how little stress was laid on the flowers and fruit at this time, from the point of view of classification. The general habit, and the shape of the leaves were the features that received most attention.
Resemblances and differences between the forms of the leaves alone must naturally appear to the botanist of the present day to be a very inadequate basis for a general system of classification. Nevertheless Mathias de l’Obel worked out a scheme on these lines which had great merit, and was a considerable advance on previous efforts. He put forward his system in his ‘Stirpium adversaria’ (1570-71) and used it also in his later work. It was thus published much earlier than the very primitive schemes of d’Aléchamps and Dodoens to which we have just referred. The best point of his system is that, by reason of their characteristic differences of leaf structure, he distinguishes the classes now known to us as Monocotyledons and Dicotyledons. He introduces a useful feature in the shape of a synoptic table of species which precedes each more or less natural group of plants. The superiority of his classification to the other arrangements in the field at the time was immediately realised. We have evidence of this in the fact that, after his ‘Kruydtbœck’ was published, Plantin brought out an album of the wood-engravings used in the book, which, although they had also appeared as illustrations to the works of Dodoens and de l’Écluse, were now arranged as in the scheme put forward by de l’Obel, “according to their genus and mutual relationship[32].”
There seems little doubt that de l’Obel made a more conscious effort than any of his predecessors to arrive at a natural classification, and that he realised that such a classification would reveal a unity in all living beings. In the preface to his ‘Stirpium adversaria nova’ of 1570 he writes—“For thus in an order, than which nothing more beautiful exists in the heavens or in the mind of a wise man, things which are far and widely different become, as it were, one thing.”
De l’Obel’s scheme is not expressed in the clear manner to which we have become accustomed in more modern systems, because, in common with other botanists of his time, he did not, as a rule, give names to the groups which we now call orders, or draw any sharp line of distinction between them.
De l’Obel’s arrangement, in spite of its good features, had serious drawbacks. The anomalous Monocotyledons, such as Arum, Tamus, Aloe and Ruscus, are scattered among the Dicotyledons, while Drosera (the Sundew) appears among the Ferns, and so on. Similarities of leaf form, which are now regarded merely as instances of “homoplastic convergence,” are responsible for many curious groupings. For instance in the ‘Kruydtbœck’ we find the Twayblade (Listera) the May Lily (Maianthemum) and the Plantain (Plantago) described in succession, while, in another part of the book, various Clovers (Trifolium), Wood Sorrel (Oxalis) and Anemone hepatica are grouped together. It is also not surprising that the Marsh Marigold (Caltha), the Waterlilies (Nymphæa and Nuphar), Limnanthemum and Frogbit (Hydrocharis) should follow one another, or that de l’Obel should have brought together the Broomrape (Orobanche), the Toothwort (Lathræa), the Bird’s-nest Orchid (Neottia) and a number of Fungi. In these latter instances the author has really arrived at genuine biological (though not morphological) groups. He has recognised, on the one hand, the marked uniformity of the type of leaf characteristic of “swimming” water-plants, and, on the other hand, he has observed the leaflessness and absence of green colour, which are negative features common to so many saprophytes and parasites.
Text-fig. 69. “Tussilago” = Tussilago farfara L., Coltsfoot [Fuchs, De historia stirpium, 1542]. Reduced.
The perception of natural affinities among plants which, in the sixteenth and seventeenth centuries, was gradually, in a dim, instinctive fashion, arising in men’s minds, is perhaps best expressed in the work of Gaspard Bauhin, especially in his ‘Pinax theatri botanici’ (1623). This work is divided into twelve books, each book being further sub-divided into sections, comprehending a variable number of genera. Neither the books nor the sections have, as a rule, any general heading, but there are certain exceptions. For instance, Book II is called ‘de Bulbosis,’ and a section of Book IV, including eighteen genera, is headed ‘Umbelliferæ.’ Some of the sections represent truly natural groups. Book III, Section VI, for example, consists of ten genera of Compositæ, while Book III, Section II includes six Crucifers. Other sections contain plants of more than one family, but yet show a distinct feeling for relationship. For instance, Book V, Section I includes Solanum, Mandragora, Hyoscyamus, Nicotiana, Papaver, Hypecoum and Argemone—that is to say four genera from the Solanaceæ followed by three from the Papaveraceæ. The common character which brings them together here is, no doubt, their narcotic property, but, although no definite line was drawn between the plants belonging to these two widely sundered families, the order in which they are described shows that their distinctness was recognised. Some of Bauhin’s other groups, however, which, like that just discussed, are distinguished by their properties, or, in other words, by their chemical features, have no pretension to naturalness from a morphological standpoint. This is the case with the group described in Book XI, Section III under the name of “Aromata,” which consists of a heterogeneous assemblage of genera belonging to different orders, which are only connected by the fact that they all yield spices useful to man.