The Rev. P. Keith on the Internal Structure of Plants. 285 



If the stem of a plant of Marigold is divided by means of 

 a transverse section, the divided extremities of the longitu- 

 dinal fibres, arranged in a circular row immediately within 

 the bark, will be distinctly perceived, and their tubular struc- 

 ture demonstrated, by means of the orifices which they pre- 

 sent, particularly when the stem has begun to wither. The 

 tubular structure of the longitudinal fibres of woody plants is 

 not so easily demonstrated. We might infer it, however, from 

 the force and facility with which the sap ascends to the very 

 summit of the stem in the spring and summer, and there are 

 some cases in which we may discern it even with the naked 

 eye. On the horizontal section of a piece of wood that has 

 been long exposed to the action of the atmosphere, the ori- 

 fices of the longitudinal tubes will appear arranged in circu- 

 lar rows in the direction of the concentric layers. Further, 

 Hedwig affirms that he observed them on the transverse sec- 

 tion of a branch of the pear-tree, detached even in the spring, 

 while the sap was yet flowing *. Hence we may believe that 

 the longitudinal fibres of plants are, in fact, longitudinal tubes 

 containing or conveying the alimentary juices. They exhibit 

 a considerable variety of structure, and have been distributed 

 by botanists into several distinct species. 



We will take them in the order, and under the anatomical 

 designations introduced or adopted by M. Mirbel, as being 

 one of the most distinguished of modern phytologists. We 

 are aware, indeed, that his anatomy of the sap-vessels has 

 been denounced as fantastical, and his theory of their origin 

 and functions as absurd; and the anatomy and theory of 

 Kieser extolled and applauded to the skies, as being of the 

 most philosophical character f. Yet we confess that we can- 

 not see the ground whether of this censure, or of this applause. 

 Whatever may be the value or fate of M. Mirbel's theory on 

 this subject, his anatomy was a signal step in advance of all 

 that had preceded it; and if succeeding anatomists have sur- 

 passed him in accuracy of research, they have been indebted 

 to his discoveries, or to his errors, for the progress they made. 

 For the rest, what do we find in the greater part of Kieser's 

 sap-vessels but the vessels of Mirbel under a different name? 

 What are we to say of his intercellular canals ; and what are 

 we to think of him as an inventor of theories, when we are 

 told that his account of the origin of the cellular tissue sur- 

 passes in absurdity even that of M. Mirbel J? We have now 

 a more formidable opponent to the theory and anatomy of 



♦ De Fibrcc Vegetabilis Ortu, sect. i. 



t Supplement to Encyc. Brit., p. 289. % Ibid. p. 304. 



