SU^' SHINE THROUGH THE WOODS. 319 



more extensive. It is likely that the root and leaf surface may 

 not increase in the same ratio as that of the cambium or growing 

 layer. 



Let us now confine our attention to any one ring the one, for 

 example, near the middle of the engraving. It is bounded upon 

 the inner and outer side by a dark line. Starting at the dark 

 inner line, the ring of wood is very porous, as shown by the multi- 

 tude of small holes giving a light appearance to this portion of 

 the ring. Farther out the wood in the ring becomes more dense, 

 until it ends in the almost solid outer dark band. This dense 

 layer is in fact the last portion of the annual ring to be formed, 

 and is laid down toward the end of the growing season. The next 

 spring a new ring begins to form just outside this dense layer, 

 and is often produced rapidly and with many large ducts and 

 vessels among the woody fibers. In short, the ring of wood in- 

 creases in density from the inside to the outside, and this being 

 followed up year after year, the most dense or autumn wood is 

 brought close to that which is the most porous, and the ring struc- 

 ture when seen in mass inevitably results. 



It is not unusual for one side of a stem to grow faster than 

 another, and then after a few years the center is toward one side 

 of the middle, and the stem is called excentric. This is quite 

 uniformly the case with all climbing stems, and the writer has a 

 vivid recollection of a microscopic study of this subject of stem 

 eccentricty in the poison ivy, for the work was interrupted by 

 the swelling and closing of the eye most engaged in the task. 

 Fig. 1 is still a fertile subject, and gives the observer a view of 

 both this eccentricity and an irregularity not uncommon in 

 stems. For some reason and it might have been one of many 

 when the stem was about ten years old a defect developed, as 

 shown upon the lower right-hand side, when each succeeding ring 

 formed quite an angle that was gradually outgrown during the 

 subsequent ten years. This blemish is shown perhaps to less ad- 

 vantage in the positive (Fig. 2). 



The points that have been brought out in the papaw stem are 

 also shown in the section of the ash. From what has been said it 

 is evident that the lower side of the picture represents the inner 

 side of the section. The center of the tree was where two pencils 

 would intersect if held with their tips to the right and left side 

 respectively of the lower edge of the engraving and at right an- 

 gles to the curvature shown by the rings of growth. The tree 

 from which the section used in the engraving was cut must 

 needs have been at least a foot in diameter, but how much more 

 can not be determined, for there is no means of knowing how 

 far it is from the outermost ring shown to the bark. This could 

 be determined in a general way from a knowledge of the ratio 



