282 Examination of the Matured Framework [BOOK u. 



existence of visible holes in the walls of cells, and points out 

 that they are not necessary for the movement of sap. The 

 dispute between Mirbel and his opponents respecting the 

 porousness of cell-walls was extended at the same time to the 

 stomata of the epidermis \ the slits in them being supposed to 

 be apertures in the epidermis regarded as a simple membrane. 

 Moldenhawer took occasion to examine the anatomy of stomata 

 more closely, and produced the first accurate descriptions and 

 figures of these organs, showing especially that the apertures are 

 not surrounded by a simple border, 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 resem- 

 blance 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 



1 On the doubts which were entertained till after 1812 on the subject of 

 stomata, see Mohl's ' Ranken und Schlingpflanzen ' (1827), p. 9. 



