CHAP, i.] by Malpighi and Grew. 243 



himself states incidentally, that he lit upon this notion from 

 looking at shrivelled masses of tissue, when he naturally saw 

 wrinkles and folds, which he took for threads. Besides he 

 seems to have used blunt knives, which might easily tear the 

 cell-walls into threads ; so we might gather from the figure in 

 Plate 40, where what he supposes to have been a tissue of 

 thread from the walls of a cell is depicted quite plainly. 

 Lastly the observation of vessels with reticulated thickening, 

 and parenchyma-cells with crossed striation may have con- 

 tributed to his view. 



It will hardly be superfluous to remark here, that Crew's 

 idea of this very delicate structure of cell-walls has evidently 

 given rise to the common expression cell-tissue (contextus 

 cellulosus) when speaking of plants and animals, an expression 

 which has become naturalised in microscopy, and is still re- 

 tained though we no longer think of Crew's comparison of 

 cell-structure with artificial lace. But the word tissue has 

 often misled later writers, as words are apt to do, and made 

 them found their conception of vegetable structure on the 

 resemblance to an artificial tissue of membranes and threads. 



Grew, like Malpighi, derives the young layers of wood in the 

 stem from the innermost layers of the rind. The true wood, he 

 says on page 114, is entirely composed of old lymph-vessels, that 

 is of fibres, which lay originally in the inner circumference of the 

 rind. But by true woody substance he understands the fibrous 

 components of the wood, excluding the air-vessels ; his lymph- 

 vessels are the bast-fibres and similar forms ; for, he goes on, 

 the air-vessels with the medullary rays and the true wood form 

 what is commonly called the wood of a tree ; he uses the term 

 air-vessels, not because these forms never contain sap, but 

 because they only contain a vegetable air during the proper 

 period of vegetation, when the vessels of the rind are filled 

 with sap. 



The above is certainly a very imperfect account of Crew's 

 services to phytotomy; for the points here made prominent 



R 2 



