as most previous observers believed, but lie between two cells, and that therefore they are not examples of the existence of pores in cell-walls, as Mirbel imagined. It may be observed here by the way, that Mirbel afterwards considered stomata to be short broad hairs; Amici in 1824, Treviranus in 1821, demonstrated their true structure by cross sections, and von Mohl at a later period investigated it thoroughly. Moldenhawer on the present occasion also enquired into the faculty attributed to stomata of opening and closing alternately, which, first observed by Comparetti, was then much discussed by the German phytotomists, and has been made the subject of repeated investigation in modern times. The whole of this discussion was in connection with the question of the pitting of cell-walls, the true nature of which Moldenhawer however never clearly understood. The peculiar vessels, known as ‘vasa propria,’ were a stone of stumbling to Moldenhawer, as they were to his predecessors and to many of his successors, because misled by the resemblance in their contents he included under this name forms of very different kinds. A very good description of the soft bast in the vascular bundle of the maize-plant is followed by a notice of the milk-tubes of Musa, the milk-cells of Asclepias which he explains incorrectly, and the milk-vessels of Chelidonium which he understood better. All these ‘vasa propria’ he took for cellular vessels, formed of tubes opening into one another; but he clearly distinguished the turpentine-ducts from them, and has given a correct figure of such a duct from the pine, though he assumes the existence of a special membrane lying inside the cell-rows which surround it, and lining the passage. Finally he passes on to the intercellular spaces, which he considers to be gaps in the cellular substance, and illustrates by Musa and Nymphaea. He does not notice particularly the narrow interstices which Treviranus had observed traversing the parenchyma. In the second portion of his work he includes all the vessels found in the vascular bundle of the maize-plant under the term spiral vessels, but he distinguishes the different forms of them well, and especially points out that rings and spirals appear on one and the same vascular tube in different parts of its course, as Bernhardi had already shown. The isolating of the vessels gave him a better opportunity of seeing how they are made up of portions of different lengths than his predecessors had enjoyed, and he proves at some length the existence of a thin closed membrane forming the vessel, but like Hedwig he places the thickenings on the outside. He as little overcame the difficulties of bordered pits as did von Mohl and Schleiden after him. In this case as in others, it was the history of development which first taught the true nature of these formations (Schacht, 1860).