WOOD AND BARK OF TREES. 
SO 
the stronger and higher was the impulse above the level j when to throw up 
I had procured glass pipes, from 150 to 200 of an inch in bore, sa ^° 
the water rose to 19 inches, and was only then stopped by the 
roughness of the interior, as I discovered upon breaking the 
pipe. Now all pipes made ly man will have this defect ; I am 
convinced, therefore, that we know not half the force of capil- 
lary attraction, as when the pipes become so diminutive, the 
roughness is of such immense consequence as to stop the flow of 
liquid ; but, in pipes formed by nature , there is no such defect , 
and the liquid will therefore rise much higher. I am the moie 
convinced of this, as the flm of the water rose near an inch 
beyond the before-mentioned height, caught on the points of interior 
the excrescences and roughness of the interior of the vessel, roughness of 
which, when exposed to the large powers of the opake solar ~ pipes * 
microscope, looked most prominent. But when to capillary 
attraction is added the perpetual motion of the root, the strong 
impetus this must give to the liquid, the additional force the sap 
vessels gain by the variation of pressure of the spiral wire round 
them, changing with each alteration of the atmosphere 5 and 
that, as the impetus must be renewed at each prominent shoot 
in a tree, it requires the capillary attraction only, to convey it 
from shoot 10 shoot : weighing all these causes well, there can, 
I think, be no doubt that they are all sufficient for throwing up 
the sap in trees ; but this is merely a hint the motion of the 
wood has drawn from me, and to be aided, I hope, by future 
discoveries, for which no diligence shall be wanting, which will, 
I doubt not, soon explain the enigma, to the satisfaction of all. 
I shall now turn to the formation of the silver grain, in which Additional 
there is a part that has greatly puzzled me. I always perceive piece to the 
that whenever I cut a transparent piece of the wood horizontally, S1 vei * 
a very diminutive row of increase appears at each stiver grain j 
this must certainly be an addition as it is fresh made wood j and 
this alone will account for the stripes that always appear between 
each yearly circle. They are from 10 to 12 in number, they 
certainly are not in the alburnum, for that shews no marks but 
what would naturally be found in every soft matter pressed 
through a pipe rather twisted ; it must, therefore, be made after- 
. wards ; but it is impossible the wood should go on increasing 
constantly at this rate, or the width would be infinitely greater 
between the yearly rows $ but if the new wood (as soon as com- 
plete) 
