plants presents difficulties at the present day to a practised observer with a good microscope. Occasionally observers had taken the stem of the gourd, where the large cells and vessels suited small magnifying power, but where many abnormal conditions occurred to interfere with their conclusions. The Monocotyledons, like the Vascular Cryptogams, had hitherto been comparatively neglected. When then Moldenhawer made a monocotyledonous and rapidly growing plant, with very large-celled tissue and comparatively very simple structure, the chief subject of his investigations, he was sure to succeed in making out many things more clearly than his predecessors. It was an important point that he found the fibrous elementary organs in this plant united with the vessels into bundles, which are separated by a strict line of demarcation from the large-celled parenchyma that surrounds them. Thus the peculiar character, the idea, of the vascular bundle was brought prominently into contrast with that of other forms of tissue. This took the place of the distinction between rind, wood, and pith, which had served former phytotomists as the basis of their histological survey, but which is in itself only a secondary result of the later elaboration of certain parts of the plant. Moldenhawer, in laying the chief stress from the first on the contrast between vascular bundles and parenchyma, hit upon a histological fact of more fundamental importance, the right appreciation of which has since enabled the phytotomist to find his way through the histology of the higher plants. For while the construction of Monocotyledons and Ferns must seem abnormal and quite peculiar to any one who starts with examining the rind, wood, and pith of old dicotyledonous stems, those on the contrary who, with Moldenhawer, have recognised a special histological system in the vascular bundles of Monocotyledons, have the way opened to them to seek for a similar one in the Dicotyledons, and to refer the secondary phenomenon of wood and rind to the primary existence of vascular bundles. Moldenhawer did in fact open this way, when he showed how the growth of a dicotyledonous stem may be understood from the structure and position of the originally isolated vascular bundles (Beiträge, p. 49, etc.). But he was thus of necessity led to the rejection of Malpighi’s theory of the growth in thickness of woody stems, which all vegetable anatomists from Grew to Mirbel had adopted. Though Bernhardi and Treviranus made weak attempts to discredit it, Moldenhawer was the first who distinctly rejected the origin of the external layers of wood from the inner bast, and proposed the first really practical basis for the later and correct theory of secondary growth in thickness (p. 35). The removal of this ancient error is in itself a very important result, and one which, apart from all other services, must secure him an honourable place in the history of botany.