347 



ing three. In a short time afterwards, granulated masses of cellular 

 tissue began to form on the upper lip of the incision made, and con- 

 tinued to extend down the surface of the bare pillar throughout the 

 summer, whilst the lower lip of the incision remained free from wood- 

 formation. The woody matter continued to increase rapidly through 

 the summer of 1840, extending itself both in perpendicular and late- 

 ral directions from the upper lip. On the lower lip two leaf-buds 

 were formed, which produced young shoots, when woody matter 

 began to form at the bases of these shoots ; but on their being 

 removed, the further increase of tissue at once stopped. In May, 

 1841, the masses of cellular tissue and wood had extended from the 

 upper lip so as to touch the lower, and to spread along its surface. 



When the junction took place, a second of the pillars was laid bare, 

 as the first had been, and the results were similar. The only differ- 

 ence observable was, that the woody matter did not form so rapidly 

 as it did in the first instance. At the expiration of three more years, 

 a second junction had taken place on the pillar last laid bare. A 

 third was now subjected to the same experiment, the principal differ- 

 ence of results in this case being that no leaf-bud was formed on the 

 lower lip. As soon as the third junction occurred, the fourth pillar 

 was treated as the others had been, the growths of young wood be- 

 coming gradually weaker on each succeeding one being the only dif- 

 ference. 



Having now detailed the way this experiment was conducted, the 

 facts elicited enable me to deduce : — 



1st. That every organ in an exogenous tree may be thoroughly 

 destroyed without causing the death of the plant, provided they are 

 gradually destroyed. 



2nd. Exogenous plants, through their vital processes, have the 

 power of again restoring the organs so destroyed. 



3rd. The formative energy takes place principally above the 

 wounded portion of the stem, and the newly-formed tissues increase, 

 for the most part, in a downward direction. 



Though these results may, at first sight, appear to be little more 

 than confirmations of the old theory of wood-formation, and even the 

 experiment itself in some degree similar to others which have already 

 been made, the latter differs materially from any I know of, in the 

 following particulars. Here the main stem of the tree was operated 

 on, and not the branches only. All the organs were destroyed, 

 including pith, medullary rays, and wood. In the course of twelve 

 years the stem of a large exogenous tree, measuring four feet nine 



