PROGRESS IN ANATOMY 77 



a paper on plant vessels about the same period. How 

 crude and even erroneous the conceptions of these days 

 were you may judge by the fact that Bernhardi mistook 

 pits for thickenings (evidently he had not learnt how 

 to focus his microscope). Rudolphi expressed his belief 

 in spontaneous generation, denied that fungi and lichens 

 were plants, and thought that stomata were surrounded 

 by sphincter muscles, while Treviranus held that inter- 

 cellular spaces were filled with sap. Still there were a 

 few points in which knowledge of anatomical structure 

 was advanced. Thus Bernhardi recognised that spiral 

 vessels had walls of their own and were not merely 

 spirally wound fibres lying in a matrix ; Link asserted 

 that cells were closed vesicles and did not communicate 

 with each other as Rudolphi thought. He also rejected 

 Rudolphi's views on stomata and said that the apertures 

 were surrounded by a cell or cells. Treviranus pointed 

 out that pitted vessels were formed by the fusion of long 

 cells placed end to end, and that all secondary thickenings 

 were laid down on the inside of the thin walls of the 

 elongated cells. He had also to his credit the discovery 

 of stomata on the capsules of mosses. 



Another anatomist, who was also a contemporary of 

 those I have just mentioned, was Mirbel, who, among 

 other publications, brought out a treatise in 1808 called 

 Exposition et defense de ma theorie de V organisation 

 vegetale. The theory he sets out to explain and defend 

 was really adopted from Caspar Wolff, whose name I 

 mentioned to you as that of the author of the Theoria 

 generationis , published in 1759. Mirbel's version of 

 Wolff's theory is that the precedent of all tissue elements 

 is a homogeneous matrix in which cells appear as 

 minute hollow cavities, and that tracheae are spirally 

 wound laminae inserted in the matrix. These elements 

 are perforated by innumerable, but invisible, pores for 

 the passage of sap from place to place. Mirbel identifies 

 laticiferous tubes, but he confounds them with resin 



