THICKENING OP SOME TREE STEMS. 19 



and next year things turned out very differently. During the 

 second summer the portion of the branch below tlie cord in- 

 creased none in thickness, or at least to no perceptible extent, 

 while all above the cord grew and thickened as if there had 

 been no interruption, and the bulging close to the cord went 

 on in the most typical fashion. 



The third season showed a continuance of what was accom- 

 plished in the second, and by the end of June there was a 

 marked difference between the thickness of the stem below the 

 binding cord and that of the portion above it. Unluckily, at 

 this stage a severe night of wind and rain became too much 

 for the heavily foliaged branch, and snapped it through at the 

 contracted part. This put a sudden end to the experiment as 

 far as that particular specimen was concerned. 



It was in March, 1901, that I cut out the ring in the 

 Sycamore stem herewith shown, so that it has had the growth 

 of two summers to produce the appearance it now has. An 

 inch and a-half below the ring it measures 5 J inches in cir- 

 cumference, while at the same distance above it the circumference 

 is 6 j^ inches. This makes nearly an inch of difference between 

 the two, as the result of growth under restrained circumstances 

 for two summers. It is interesting also to see that the upper 

 portion shows two rings of wood more than the lower, the former 

 having seven, while the latter has only five. In both it can 

 be observed that the fourth is the greatest, so that this tree 

 must have had a particularly favourable growth in the year 

 1899. The result of the last cold summer (1902) is that the 

 final ring on the upper portion is decidedly smaller than any 

 of the others. 



Experiments of this kind have long been used for a double 

 purpose — firstly, to show that the ascending sap is conveyed 

 through the wood; and, secondly, that the assimilated sap 

 passes through the bast. The first point is established by the 

 fact that the leaves go on as if no interruption were made, 

 and even if you cut out a ring of bast, as I have done from a 

 Sycamore, when the tree is in full leaf in summer, the leaves 

 show no sign of drooping. Then the check to the thickening 

 of the stem below the ring shows that the supply from above 

 has been cut off. 



