6i5 



forms composing the annual ring. The growth of the medullary, or the 

 bark rays, only exceeds that of other tissues in all processes of ivound heal- 

 ing; it thereby becomes predominate. 



Also if, in the above mentioned "moon rings," the boundaries between 

 the already destroyed parenchyma wood of the annular bands and the 

 healthy tissue are investigated, not infrequently a striking widening of the 

 medullary rays is found, especially in oaks. 



In conifers, especially pines, a still more extreme form of disturbance 

 may be found, the so-called "ring-barking." At times, when the trunk is 

 split, a complete cylinder, beginning at the healthy central portion of the 

 trunk, separates from the apparently equally healthy peripheral wood, as 

 from a shell. This takes place because the tissue is destroyed in one, and 

 indeed only one annual ring, becomes rotten and traversed by mycelium. 



This form of ring barking is distinguished by its sound, healthy core 

 from the one studied by Robert Hartig^ in the pine, in which a wound 

 parasite, Trametes Pini (Brot.) Fr. causes the destruction of the core but 

 does not extend into the healthy sap-wood. Hartig describes the rapid 

 advance of the mycelium in the medullary rays and, after having discussed 

 the destruction of the wood caused by the mycelium, the dissolution of the 

 incrusting substances and the retention of the cellulose in the wood fibres, 

 says that, "as the result of the collapse of the wood which is connected with 

 this decay and loss of water, not only are radially extending cracks formed 

 but often the outermost annual layers are loosened as a mantel from a 

 thicker or thinner core. Thus annular clefts are produced which can have 

 led to the name of "ring barking." We are here, therefore, concerned with 

 a form of very extensive red rot, or heart rot. According to v. Tubeuf, 

 the fungus appears also in spruces and has been observed in larches and 

 white firs and, in America, in the Douglas fir. Emphasis should be laid 

 on the fact that this mycehum spreads "very easily in one certain annual 

 zone- and the diseased, white tissue aggregations, which now consist only 

 of cellulose, may be found abundantly in the spring wood"^. This seems to 

 me to indicate that the fungus finds greater resistance in the adjacent annual 

 rings, i. e., the annual ring already attacked must necessarily have been 

 more porously constructed. Accordingly, bands of parenchyma wood 

 might contribute especially not only to infection of branch wounds by 

 Trametes and other wood destroyers, but also to their distribution in the 

 trunk. 



False Annual Rings. 



Double Rings, Etc. 



Its is a well known fact* that the size and constitution of every annual 



1 Hartig, R., Wichtig-e Krankheiten der Waldbaume. Berlin 1874, p. 55. 



2 V. Tubeuf, Pflanzenkranlclieiten durch Icryptogame Parasiten vei-ursacht. 

 Berlin 1895, p. 471. 



8 Hartig-, R., Lehrbuch der Pflanzenkrankheiten. Berlin 1900, p. 172. 

 * Kiister, E., Pathologische Pflanzenanatomie. Jena 1903. p. 25, etc. Here also 

 pertinent bibliography. 



