[PENIL4.LLOW] A BIRCH ROPE 245 



2. It does not extend to the outermost layers of cork which were 

 the first in development, but it terminates several layers below the 

 general surface of the structure (fig. 8.) 



3. Where nodal areas of parenchyma tissue are developed, the 

 outermost one is always the smaller or smallest as the case may be (fig. 

 9), the size increasing in centripetal order. 



•i. In the growth of the structure, the development of the cork 

 has progressed centripetally and in such a way that the tension between 

 the outer and inner regions steadily augments. 



From the facts thus recited, it would be reasonable to conclude that 

 the development of the fan-shaped areas of dense and modified cork, as 

 well as the development of the nodal areas, is a direct response to condi- 

 tions of tension attendant upon the formation of the inelastic cork mem- 

 branes. 



Conclusions. 



Upon the basis of the foregoing facts, we are now in a position to 

 consider an explanation of the peculiar growth under examination, so 

 far as an explanation may be possible; but unfortunately we are not in 

 possession of some of the most essential facts with respect to the special 

 features which characterized the specimen in situ. In the absence of 

 such facts, it is impossible to draw important inferences from its struc- 

 ture ; and although we may not be able to ascertain the determining cause 

 of such a peculiar development, we can determine certain aspects of its 

 formation with accuracy, and from the conclusions so obtained, draw in- 

 ferences which may prove of value as suggestions with reference to the 

 possible solution of allied phenomena. 



The question as to 'how and under what conditions the growth ori- 

 ginated, is perhaps beyond the possibilities of successful solution at pre- 

 sent, but in our efforts to reach an answer, it may be well to first of all 

 examine into the bearing of the internal structure. As already 

 pointed out, there is a" complete absence of anything which can be inter- 

 preted as an evidence of intermittent, longitudinal growth, since there 

 is an entire absence of nodes or of rings or scars which would mark suc- 

 cessive periods of development, such as would be found in the leaf scars 

 and nodes upon young branches of the same tree. From this circum- 

 stance we are led to infer that the entire growth in length must have 

 been accomplished within the limits of one season. This conclusion is 

 greatly strengthened by certain other observed facts. The structure as 

 a whole is very slender, according in this respect with very rapid de- 

 velopment. Furthermore, the absence of lenticels or other respiratory 



