14 PITH-EAY FLECKS I:N^ WOOD. 



flecks are the principal starting points in gummation. His observa- 

 tions have been confii-raed by more recent investigations. 



In the present studies of the wood of cherry some mines were found 

 filled with wound tissue of the usual type, while in others gummation 

 was well under way (PL VI). There was apparently no distinction 

 in species or individuals as regards the formation of gum. All species 

 of cherry subject to pith flecks are also susceptible to the breaking- 

 down process. This can be expected from the results obtamed by 

 Mikosch and Rant.^ 



The discolored spots produced by gummation in cherry wood often 

 render it unfit for the finer grades of furniture. This defect is often 

 directly traceable to pith flecks. ^^Tlere the mines remain occluded 

 with normal wound tissue, little injury results, owing to the similar 

 coloration of the surrounding wood with that of the wound tissue. It 

 is with the inception of gummation that the injury reafly begins. 

 The disintegration thus started often spreads until the sound tissue is 

 afl'ected. 



REFERENCES. 



BouLGER, G. S. Wood (2d edition), p. 33. 1908. 



CoRDES. HetZamensteldervoornaamsteEuropescheHoutsoorten. Haarlem. 1857. 



DE Barry, A. Vergleichende Anatomie der ^'egetatiollsorgane der Phanerogameu 



imd Fame, pp. 492-498. Leipzig. 1877. 

 Gayer, K. Schlich's Manual of Forestry, Vol. V, London. 1908. 

 Grossenbacher, J. G. Medullary Spots. A Contribution to the Life History of 



Some Cambium Miners. New York Agr. Exp. Sta., Tech. Bull. 15, Geneva, 



N. Y. 1910. 

 Haberlaxdt, G. Physiologische Pflanzenanatomie, p. 606. Leipzig. 1909. 

 Hanausek, T. F. The Microscopy of Technical Products (English edition), pp. 



205-206. 1907. 

 Hartig, Robt. Die Unterscheidungsmerkmale der wichtigeren in Deutschland 



wachsenden Holzer. Miinchen. 1879. 

 Hartig, Robt. Lehrbuch der Anatomie imd Physiologie der Pflanzen, pp. 92-93. 



1891. 

 Hartig, Th. Forstliche Cultm-pflanzen. 1840. 

 Hartig, Th. Vollstandige Natm'geschichte der forstlichen Cultm-pflanzen Deutsoh- 



lands, pp. 228, 326, 336. Berfm. 1851. 



1 As previously noted, the larvse lire in the cambial zone and destroy the growing or dividing cells by 

 sucking their contents. The burrow thus formed by the lar\-a is partially filled with the remnants of dead 

 cell walls and excrement of lar\-?c. It is still open to doubt ^^ hether gummation begins immediately before 

 the wound tissue forms or whether the latter first fills the mines and then breaks down. Mines were found 

 which presented all stages of development. Some were completely filled Avith normal wound tissue; while 

 in others disintegration had affected a part of the cells. In some instances no wound tissue was in evidence; 

 here the mines in cross section appeared like openings in the otherwise normal tissue. It is difficult to say 

 whether the gum in sitch instances arose from the liquefaction of the dead cell walls or, as is more probable, 

 from the wound tissue formed subsequent to the passage of the lan^te. Either theory may be reconciled 

 with the deductions of Mikosch and Rant. 



Regarding Ruhland's theory- concerning the necessity of oxygen in the process, little can be said. It 

 perhaps accounts for the absence of gum formation in some of the mines. Where gummation does occiu" 

 it can hardly be ascribed to atmospheric oxygen. It is highly improbable that the latter vould penetrate 

 the mine for any great distance, owing to the small opening at its inception and to the rapid formation of 

 woimd tissue after the passage of the larva. 



