GREW 169 



the vesicles of bread, and supposes to have originated 

 in the fermentation of a "coagulum." Hooke had called 

 the cells of a parenchyma a "heap of bubbles"; Grew's 

 favourite term is " bladders." He knows that " a 

 single row or file of bladders, evenly and perpendicularly 

 piled, may sometimes . . . break into one another and so 

 make one continued cavity" (p. 118), an anticipation of 

 Mohl's discovery of 1831. His notion of the cell- wall, 

 suggested by the thickenings so frequent in vessels, was 

 that it consisted of a network of fine threads. 



Vessels 



Grew discovered and traced the vessels of the bean- 

 seedling and other plants, but first learned from Malpighi 

 that some of them possess a spiral thread. He remarks 

 that spiral vessels never branch, and that they may 

 extend to great distances. His " lymph-ducts " are 

 not true vessels, but bast-fibres, &c. 



Monocotyledonous Stem 



We find a good figure of a transverse section of a 

 maize-stem, and Grew notes the scattered vascular 

 bundles, as well as the lack of a distinct bark and pith 

 (p. 104, PL XVni, Fig. 2). 



Resin-passages 



He recognises and correctly interprets the resin- 

 passages in the cortex of a pine-stem (p. 1 1 0). 



Resistance to Bending of Hollow Structures 



The rigidity of a circumferential zone of vascular 

 bundles, as well as the rigidity of quills and hoUow^ 

 bones, when compared with solid rods of the same length 

 and the same weight, is pointed out (p. 23). 



