RESULTS OF GIRDLING. 175 



than a hundred years that the crude sap ascends in the wood, 

 especially in the sap-wood, and that the elaborated sap 

 descends in the bark. This seemed to be proved by the fact 

 first observed by Magnol, that colored liquids absorbed by 

 plants rise unchanged through the wood, but not through the 

 bark, and also by the fact that if a ring of bark be removed 

 from a growing stem, it ceases to increase below the ring, 

 but forms a swelling at the edge of the bark above the ring. 

 It was observed also that the bark of those trees which, like 

 the birch, bleed freely from a fresh wound in the wood in 

 spring, is always at this season comparatively dry and free 

 from sap. 



Knight experimented upon the potato-plant, and discovered 

 that when a ring of bark was removed from the stem no 

 tubers were formed under ground, or below the ring, but 

 small tubers appeared in the axils of the leaves above the 

 ring, and the plant remained fresh and vigorous, and when 

 the axillary tubers were taken off, blossomed and bore fruit. 



Further proof of the downward, or rootward, tendency of 

 the elaborated sap is seen in the effect of ringing a fruit- 

 bearing branch of a grape-vine or pear-tree, by which the fruit 

 is increased in size through the abundance of nutriment which 

 under ordinary circumstances would descend to the lower part 

 of the plant. 



Professor Rainey, of London, describes an interesting 

 experiment, performed by him on some young lilacs, which 

 seems to prove conclusively that the crude sap rises in the 

 wood, and the j)erfected sap, which is essential to the life of 

 the plant, descends only in the bark or the cambium lay^r just 

 beneath it, and that it is incapable of penetrating the sap- 

 wood or any other tissye. He selected four shoots or sprouts 

 of a similar character, and around three of them he wound 

 firmly a coil of copper-wire, but without breaking the bark. 

 This was in December, 1844. In the spring of 1845, all 

 four of them expanded their leaves at the same time, and 

 continued through the season equally healthy. One of them 

 was now cut for examination, and exhibited a layer of wood 

 and a layer of bark of the usual thickness above the ligature, 

 while below, the layers, thongh visible, were very thin. The 

 next spring, 1846, the two remaining shoots put forth their 



