1033 



passage of the fluid of one cell into another by endosmose during a 

 period of a fortnight or three weeks. For this imaginary state of 

 progressive inspissation of the contents of the cells, according to their 

 relative distance from the roots, could only be the result of a vital 

 process ; and therefore, if the ascent of the sap depended upon it, 

 that ascent must immediately cease in any part of a stem as soon as 

 its vitality is destroyed. 



" 27. The preceding explanation of the cause of the ascent of the 

 sap being made to depend upon the foliaceous organs, pre-supposes 

 that they exist before the sap can begin to ascend. This, without 

 doubt, is true, although in some cases it may seem not to be so, as 

 these organs appear, at some seasons, from their minuteness and im- 

 perfect state of development, to be entirely absent ; yet, notwithstand- 

 ing, their existence is unquestionable and their function similar to 

 that of the matured leaves. These parts, before they acquire the 

 general characters of leaves, are more or less concealed and denomi- 

 nated leaf-buds ; their form is conical. They consist of a central 

 axis composed of cells and a few vessels continuous with those around 

 the pith of the branch on which they are situated, and surrounded 

 by rudimentary leaves. The cells resemble those of the pith in hav- 

 ing very thin cell-walls and but little intercellular tissue, and in the 

 external cells generally containing starch granules or some other so- 

 lid matter. Now, as these germinating bodies (the leaf-buds) require 

 a supply of water the instant their germination commences, and the 

 solid material within their cells becomes elaborated and a solution 

 formed, that is, the instant the conditions required for endosmose are 

 set up, it is necessary that they should be situated near to a reservoir 

 of that fluid : this is efl'ected by their connexion with, and their prox- 

 imity to, the pith ; so that the ofiice of the pith is most probably to 

 contain between and within its cells that portion of water which the 

 leaf-buds require the moment their transformation into leaves com- 

 mences, and before their development is sufficiently advanced to en- 

 able them, by the absorbing power of their own intercellular tissue, 

 to absorb it from the surrounding tissue, in the manner described 

 when treating of the ascent of the sap into the matured leaves. 

 Hence the reason why the pith is so universally connected with leaf- 

 buds, and why it occupies the central portion of the ascending axis 

 and those parts derived from it, and is absent in the roots." — p. 12. 



The author, considering he has proved the ascent of crude sap in 

 a tissue surrounding the cells as well as entering the structure of 



