348 PHYTOLOGT. 



a part rendered weak, and the stimulus of the necessity of growth takes 

 place here. Or it may be put in this light : the part near or close to 

 the barked part is conscious of the injury done on one side, and con- 

 scious of what is to be supported on the other, therefore it sets to work 

 accordingly, that it may be able to do the last [support the parts 

 above 1 ]. 



The part between the root and the barked part growing but very 

 little, is also easily explained : for by admitting that the communication 

 between the two parts is cut off, then it is only reversing the above 

 theory, viz. its not being conscious of any part beyond it, as if it had 

 been cut quite through, as was mentioned in page [345], 



April 1775 I made the following experiment: — I slit the bark of a 

 branch of a Scotch Fir for about two inches in length, and separated 

 the bark from the wood all round, and put a piece of card round be- 

 tween the bark and the wood to keep them separate, — the slits allowing 

 me to pass the card all round. This branch shot out as long shoots as 

 any of the others in the same circle, but it died in the winter. 



I did the same with a Laburnum : one of the slits of the bark formed 

 wood in its inner surface, and the branch lived. 



The same with a Lilac. The flowers of this branch did not blow 

 so soon as those on the other branches, nor did they come to perfection. 

 The leaves were of a paler green than those of the other branches. 



Of the Growth of Trees. — Trees and shrubs grow in thickness by a new 

 layer of wood being laid every year on the outside of the last year's, 

 immediately on the inside of the bark ; and, as the new layer is at first 

 but slightly attached to the last year's layer, but every year becomes 

 firmer and firmer in its attachment, I find that, when the branches are 

 cut off in the autumn, after this outer layer is completely formed, such 

 layer, in the stem, will not attach itself to the last year's layer until 

 the following year ; and even then it will not be attached strongly, 

 because this year's shoots are not such as give great influence to the 

 action of the stem. 



As wood grows by a new layer being formed every summer on the 

 surface of the old, and as each layer is several months in forming, the 

 first formed part, of every layer has the whole summer to perfect itself 

 in, and so on less and less, as the succeeding parts are later and later 

 in forming ; so that the last formed part has but little time in the 

 summer to become good wood ; therefore each layer is made up of wood 



1 [This paragraph is eminently characteristic of Hunter's peculiar mode of phy- 

 siological thought, and of his tendency to personify phenomena.. The greater growth 

 aboTe the barked part is due to the arrest, at that part, of the descending nutritive 

 currents of the carbonized sap.] 



