FOUNDATIONS OF ANATOMY 33 



fluid is heterogeneous before it enters and becomes more 

 so afterwards. In the cortex it ferments and the first 

 result is the separation of a scum which passes outwards 

 and becomes the skin. In its transit through the cortex 

 the sap is filtered, at the same time the cortex is distended 

 and new fluids enter. The filtered sap passes to the wood 

 and has there added to it such extractives as the wood 

 can provide. It now becomes " cambium " or refined 

 plant juice, some of which is incorporated in the wood 

 itself. By a kind of peristalsis the wood then pumps the 

 remainder back to the cortex to be used in part as nutri- 

 ment by that tissue ; what is left over, " the second 

 remainder," is discharged to the skin to nourish it in turn.x 



Grew next discusses the stem in the same way, recog- 

 nising here also skin, cortical body, ligneous body, 

 insertions, and pith. The ligneous body attracts his 

 attention more especially ; he describes the annual rings 

 and likens the innumerable and " extraordinarily small 

 vessels or concave fibres " of which it is composed, 

 together with the " cortical insertions " or medullary 

 rays, to the warp and woof of a piece of cloth. He 

 searched in vain for valves in the vessels that might serve 

 to direct the sap flow, but he presents us with the same 

 strange notions about sap circulation in the stem that 

 I have summarised apropos of the root. The upward 

 movement of the sap is accounted for by capillarity aided 

 by a force which suggests the pressure of turgid paren- 

 chyma, anticipating in a way the views of Godlewski 

 and Westermaier two hundred years later. " And the 

 said pipe or vessel/' he says, " being all along surrounded 

 by the like bladders, the sap therein, is still forced 

 higher and higher ; the bladders of the parenchyma 

 being, as is said, so many cisterns of liquor, which transfuse 

 their repeated supplies throughout the length of the 

 pipe." He proved experimentally that the path of ascent 

 was by the wood, but said that this path was followed in 

 spring only, " for the greater part of the year, it riseth in the 



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