THE INJECTED TRUNKS OF CHESTNUT TREES 491 



side. He produced this result by cutting away a part of the seed- 

 lings' stems, when they were actively growing. 



Schilberszky's result, obtained by cutting, was produced by the 

 injections, w^hen the solutions were toxic enough to kill or to retard 

 the activities of the fibro-vascular bundles and the cambium layer. 

 But the forms assumed by the deranged tissues, resulting from the 

 injections, were not as definite as those obtained by the knife. This 

 was probably for the reason that the toxic solutions did not usually 

 make definite wounds, but killed only groups of cells or single cells, 

 while other groups were simply retarded in growth or even stimu- 

 lated. Also the shock from the incision was a single one, while in 

 the case of the injections the source of irritation was present for 

 weeks or months. 



As stated before, Schilberszky found the extra-fascicular vas- 

 cular bundles developed from the starch sheath, which is situated 

 just outside the bast-fiber cells in the case of the pea and bean 

 seedlings. This row of cells produced both phloem and xylem 

 tissue. 



In the case of the injections the result cannot be attributed to the 

 stimulation of a single tissue but rather of three: phloem, cambium 

 and xylem. So far the examination of the trees has not shown a 

 development of new extra-phloem cells. The xylem cells found in 

 the phloem region appear to have been produced by cell division of 

 the phloem cells followed by lignification, or by a lignification of the 

 original phloem cell walls. The isolated groups of xylem usually 

 commenced to develop just behind the groups of bast-fiber, and 

 this might indicate that the cells there were meristematic or cells 

 which retained unusual regenerative powers. It has not been known 

 hitherto that they were meristematic cells. It seems more probable 

 from the way in which the groups of xylem cells increase, that these 

 phloem cells first respond to stimulation because of their position 

 behind the bast-fiber groups. Osmosis in the case of the bast-fibers 

 must be extremely slow. Therefore, an irritant coming from the 

 direction of the injected chemical would strike the cells situated just 

 back of the bast-fibers from two sides at once. Those phloem cells, 

 exposed directly and from one direction, would respond more slowly 

 by a lignification of their cell walls. 



