264 Examination of the Matured Framework [BOOK n. 



In the work just mentioned Bernhardi treats of other forms of 

 tissue as well as vessels, and endeavours to distinguish and 

 classify them more exactly than had hitherto been done. He 

 contrasts favourably with his contemporaries in the fact, that 

 he sought to define the histological terms employed as precisely 

 as possible, a great step in advance at a time when phytotomic 

 conceptions were in a very misty condition. He distinguishes 

 three chief forms of vegetable tissue, pith, bast, and vessels. 



By pith he means the tissue which Grew had named paren- 

 chyma, and which is still so called ; it remained a question 

 with him whether the cells of the pith are pierced by visible 

 pores. By the word bast he understood not only the fibrous 

 elements of the rind, but those of the wood also, and in general 

 what is now known as prosenchyma ; this agrees very well with 

 Malpighi's view, which was adopted by Bernhardi and by all his 

 contemporaries, that the inner layers of the bast are changed 

 into the exterior layers of wood to make the increase in thick- 

 ness of the woody stem ; but he did not admit the same origin 

 in the case of the innermost portion of the wood, for this is 

 formed from the first in the young shoots, which alone contain 

 true spiral vessels with threads that may be wound off. 



Bernhardi distinguishes vessels into two main groups, air- 

 vessels and vessels properly so called. He calls the first 

 group air-vessels for the same reason that led Grew to give 

 them that name, namely, that they are filled with air during a 

 part at least of the period of vegetation ; they are found in the 

 wood, and, where there is no closed woody body, there the 

 woody bundles are formed both of vessels and also of bast 

 strands which enclose vascular canals. These latter he next 

 divides into three chief kinds ; annular vessels, which he was 

 the first to discover, true spiral vessels with a band which can 

 be unwound, and scalariform vessels, by which term he under- 

 stood not only those with broad slits, such as are found in 

 Ferns, but also the pitted vessels in secondary wood. His 

 idea of annular and spiral vessels was perfectly correct, and he 



