IV.] VARIOUS THEORIES, &c. 105 



are self-supporting — ie. they must obey the law 

 of capillarity, and remain suspended in the tube. 

 That the chaplets exist is a fact of observation, 

 though we do not know their length. 



Now consider the system as simplified in a diagram. 

 Suppose a vessel, in contact with medullary rays and 

 wood-parenchyma at different levels. Water rises 

 in the vessel to a given height, the level of the first 

 medullary ray, and is held there by the pressure 

 from below. The parenchyma at that level then 

 uses this water as a store from which it draws by 

 endosmose. 



At a somewhat higher level, and in contact with 

 the same vessel, is another medullary ray, the cells 

 of which are wanting in water : they take water by 

 endosmose from parenchyma-cells lower down in the 

 wood, the action reaching to the medullary ray first 

 considered. This absorbent action goes on till 

 these cells of the higher medullary ray also are 

 turgid, and so rich in water that they exfiltrate it 

 into the neighbouring vessel, where the air is rarefied. 

 Here — te. at a higher level — the expressed water 

 collects into a small column, growing in both direc- 

 tions upwards and downwards. This will be sup- 

 ported by capillarity until it reaches a certain length, 

 and before it exceeds this the action will have 



