248 ROYAL SOCIETY OF CANADA 



as the older i3arts avouIcT have matured as rapidly as formed ; but on the 

 contrary we find the cork layers to be developed longitudinally, and all 

 the evidence points to a simultaneous activity throughout the entire 

 length. We must therefore dismiss the theory of basal growth as being 

 inconsistent with, and, indeed, opposed to the facts. 



2. The second alternative is terminal growth. If the elongation 

 were to depend entirely upon activity of the cells at the apex, then it 

 would still be possible for all the more inferior parts to continue active 

 until the close of the season, but two very substantial facts seem to be 

 opposed to this view. In the first place, unless the rate of growth were 

 far greater than we have any reason to suppose was the case, and indeed 

 far greater than would be probable under the climatic conditions of the 

 locality, the length attained would not have been completed within thp 

 limits of one season as there is good reason to suppose must have beeo 

 the case. In the second place, under the influence of such terminal 

 growth, the basal portions would have matured much in advance of th<? 

 terminal parts, even while the latter were continuing to elongate. There 

 is no direct evidence in the specimen to prove that such may have been 

 the case, but on the contrary the strictly parenchymatous character of the 

 basic structure seems to point to an opposite conclusion. 



3. We are thus brought to our third alternative, according to which 

 we may suppose that as the tumour emerged from the bark, it was com- 

 posed wholly of very active parenchyma tissue which continued to in- 

 crease in volume as such a tissue would naturally do when reacting to a 

 traumatic stimulus. Under such circumstances, each cell would parti- 

 cipate in the process of division, and thus through division and enlarg- 

 ment of the individual cells, the tumour would not only increase rapidly 

 in volume, but at such a rate as would render its completion within a 

 comparatively short time, a definite possibility. This would seem to my 

 mind, the most satisfactory explanation which the observed facts will 

 warrant. On this basis it becomes possible to account for the develop- 

 ment of the cork which obviously proceeded centripetally, and nearly 

 if not quite simultaneously throughout the entire length of the tumour. 



The only other consideration that needs to be dealt with, is the 

 structural alteration of the cork layers due to compression. It has been 

 shown that each layer of cork was influenced by compression in such a 

 way that the outer cells are always radially narrower than the inner- 

 most, an alteration also eshibited between the outermost and the inner- 

 most layers in such way that the cells of the latter are two and one-half 

 times broader than the former. Otherwise this observation is supported 

 by the fact that the innermost layers of cork are approximately three 

 times thicker than the outer layers. But it is also probable that this 



