Albertus Magnus, who kept alive in the Middle Ages the spirit of Aristotelian botany, was more advanced than Theophrastus in his method of classification. It is true that he divides the vegetable world into Trees, Shrubs, Undershrubs, Bushes, Herbs and Fungi, but at the same time he points out that this is an arbitrary scheme, since these groups cannot always be distinguished from one another, and also because the same plant may belong to different classes at different periods of its life. A study of the writings of Albertus reveals the fact that he had in mind, though he did not clearly state it, a much more highly evolved system, which may be diagrammatically represented as follows. The modern equivalents of his different groups are shown in square brackets:— [Illustration: Text-fig. 63. “Carui” [Ortus Sanitatis, Mainz, 1491].] I. Leafless plants [Cryptogams in part]. II. Leafy plants [Phanerogams and certain Cryptogams]. 1. Corticate plants [Monocotyledons]. 2. Tunicate plants [Dicotyledons]. (_a_) Herbaceous. (_b_) Woody. The word _tunicate_ in the above table is used for the plants which Albertus describes as growing “ex ligneis tunicis.” It seems clear from this expression that he realised that there was an anatomical distinction between Dicotyledons and Monocotyledons. Considering how much Albertus had achieved, it is somewhat curious that Cesalpino, who represented Aristotelian botany in the sixteenth, as Albertus did in the thirteenth century, should have produced so inadequate a system as his own contribution to the subject. We owe to him one marked advance, the recognition, namely, of the importance of the seed. On the whole, however, his classification savours too much of having been thought out in the study, and it suffers by comparison with other systems of about the same period, such as those of de l’Obel and Bauhin, which were arrived at rather by instinct, acting upon observation, than by a definite and self-conscious intellectual effort. Cesalpino makes his main distinction, on the old Aristotelian plan, between Trees and Shrubs on the one hand, and Undershrubs and Herbs on the other. He divides the first of these groups into two, and the second into thirteen classes, depending chiefly on seed and fruit characters. Very few of these classes really represent natural groups, and the chief of all distinctions among Flowering Plants, that between Dicotyledons and Monocotyledons, which was foreshadowed by Albertus, is almost lost to sight.