Chap, hi.] of Cell- membrane in Plants. 269 



Link is more happy in taking the part that surrounds the 

 aperture for a cell, or a group of cells. Rudolphi considers the 

 great cavities in hollow stems and in the tissue of water-plants 

 as the only air-passages in plants ; Link explains these cavities 

 as gaps caused by the irregular growth of cellular tissue. With 

 Rudolphi the word vessel means not only vascular forms in 

 wood, but milk-vessels and resin-ducts also, and to the 

 former he even transfers Malpighi's view of the structure 

 of spiral vessels. Link designates the tubes of the wood 

 only as vessels, combining the most various forms of them 

 under the term spiral vessels ; he excludes milk-vessels, resin- 

 ducts, and the like from the conception of a vessel, and in this 

 he is somewhat inconsistent, since he assumes with Rudolphi 

 that a vessel, in plants as in animals, is a canal for the con- 

 veyance of nutrient sap. 



With all these contradictions, the two essays agree in adopt- 

 ing the old Malpighian view of the growth in thickness of stems, 

 according to which the new layers of wood are formed from the 

 inner layers of bast, while between the bast-cells, which are 

 here taken to be identical with woody fibre, new spiral vessels 

 arise contemporaneously, and, as Link expressly says, from 

 juices which pour out between the bast-cells. 



It is hard to understand how two treatises, so contradictory 

 as they have been shown to be, could have both received 

 a prize at the same time, or how the great difference could 

 have been overlooked between Link's sensible and well- 

 arranged account of his subject, and Rudolphi's uncritical 

 statements, which everywhere rely more on old authority than 

 on his own observation. It is however certain that Link's 

 better production is inferior to Bernhardi's treatise, unless we 

 choose to consider the greater copiousness of detail in Link. 

 the number of his observations, and his acquaintance with the 

 literature of the subject, as giving him the advantage. His 

 figures, as well as Rudolphi's, are not so good as those of 

 Bernhardt. 



