6 4 



attempt, in any way, to retain and hold it as a cellulose wall does. 

 It only takes it up and gives it up again in very small quantities, 

 however. The ordinary cellulose cell-walls, on account of their 

 property of levying black mail upon any fluid that passes into 

 them, and retaining a considerable quantity of the water in them- 

 selves, are not good conductors of fluid. The lignified cell-wall, 

 on the other hand, is a good conductor, as it must pass on what- 

 ever fluid it gets, since it cannot absorb it into itself. A very 

 slight pressure, then, on the part of the parenchyma cells of the 

 root, is sufficient to make the lignified cell-walls take up water 

 from them, and when this fluid has got into the lignified wall, it 

 exists there in a very mobile condition, and can be readily passed 

 on. 



The fluid in the walls of fibro-vascular tissue in the leaves, is 

 constantly being drawn upon by the parenchyma cells of the leaves 

 which are actively transpiring. In consequence of this, the vessel 

 walls become poor in water, and exert a drawing influence on the 

 water in the walls of the remainder of the vascular system ; this 

 influence extends down the leaf-stalk into the branch, and thence 

 into the stem, and finally to the vessels of the root. If the fluid 

 which exists in the lignified cell-wall, was in a similar condition 

 to that of the water in a cellulose one, the supply of fluid 

 to meet the demand created by transpiration could not be 

 maintained with sufficient rapidity, but since it exists in a con- 

 dition in which it can easily be passed along, this enables the 

 necessary supply to be kept up through a long branch. 



If an ordinary branch of pinewood, a yard in length, be taken, 

 and the surfaces of its two ends having been rendered perfectly 

 smooth, be then carefully dried, and after this a little moisture is 

 spread on the upper surface by means of a brush, at the same 

 moment as the application is made, a distinct appearance of liquid 

 poured out at the other extremity will be observed. From this 

 simple experiment we can derive some idea as to the state of 

 things existing in the living plant, and thus we see that a with- 

 drawal of water, however slight, at one point, is accompanied by 

 an absorption of water at another. The liquid in the lignified 

 cell-walls forms then an unbroken column, from the leaves down 



