144 ON THE INCONVERTIBILITY 



their colours, I took off, early in the spring, portions of bark of equal 

 length, from branches of equal size, and I transposed these pieces of 

 bark, inclosing a part of the stem of the apple tree with a covering of 

 the bark of the crab tree, which extended quite round it, and applying 

 the bark of the apple tree to the stem of the crab tree in the same man- 

 ner. Bandages were then applied to keep the transposed bark and the 

 alburnum in contact with each other ; and the air was excluded by a 

 plaster composed of bees- wax and turpentine, and with a covering of 

 tempered clay. 



The interior surface of the bark of the crab tree presented numerous 

 sinuosities, which corresponded with similar inequalities on the surface of 

 the alburnum, occasioned by the former existence of many lateral 

 branches. The interior surface of the bark of the apple tree, as well as 

 the external surface of the alburnum, was, on the contrary, perfectly 

 smooth and even. A vital union soon took place between the transposed 

 pieces of bark, and the alburnum and bark of the trees to which they 

 were applied ; and in the autumn it appeared evident, that a layer of 

 alburnum had been, in every instance, formed beneath the transposed 

 pieces of bark, which were then taken off. 



Examining the organisation of the alburnum, which had been gene- 

 rated beneath the transposed pieces of bark of the crab tree, and which 

 had formed a perfect union with the alburnum of the apple tree, I could 

 not discover any traces of the sinuosities I had noticed ; nor was the 

 uneven surface of the alburnum of the crab tree more changed by the 

 smooth transposed bark of the apple tree. The newly generated albur- 

 num, beneath the transposed bark, appeared perfectly similar to that of 

 other parts of the stock, and the direction of the fibres and vessels did 

 not in any degree correspond with those of the transposed bark * . 



Repeating this experiment, I scraped off the external surface of the albur- 

 num in several spaces, about three lines in diameter, and in these spaces 

 no union took place between the transposed bark and the alburnum of 

 the stock, nor was there any alburnum deposited in the abraded spaces ; 

 but the newly generated cortical and alburnous layers took a circular, 

 and rather elliptical, course round those spaces, and appeared to have 

 been generated by a descending fluid, which had divided into two 



* Duhamel having taken off, and immediately replaced, similar pieces of the bark of young 

 elms, subsequently found that the alburnum, which was generated beneath such pieces of bark, 

 had not formed any union with the alburnum of the tree beneath it. But this great naturalist 

 did not employ ligatures of sufficient power to bring the bark and alburnum into close contact, 

 or the result would have been different. 



