330 



These alternating tissue layers are separated by broad curved medul- 

 lary rays (mst) which even in the entirely healthy bark can exhibit a wavy 

 course, but in the diseased bark may often be displaced and take a hori- 

 zontal course. The sharp curvature is caused by the spreading apart of the 

 parenchyma cells which, containing chlorophyll and lying between the slen- 

 der bands of wedge cells, elongate into pouches, and for a long time contain 

 a great deal of starch. They also press outward the hard bast bundles and 

 the rows of oxalate crystals. This great layer of separation is covered by a 

 plate cork layer extending irregularly into the tissue and often accompanied 

 by full cork (J) and the suberized bark tissue cut off by it which belonged 

 to the earlier period of growth (k). The cork layer often curves spherically 

 into the pouch-like spongy tissue (sp) and forms the hard, crater-like points 

 on the under side of the loosened bark scale, which were mentioned at the 

 beginning of this description. The process of loosening the bark tatters is 

 completed on the boundary between the hard tissue of the suberized cortex 

 of the previous year, and the soft pouch-like parenchyma. The upper sur- 

 face of the separating cushions appears woolly and rough, or smooth, 

 according to whether the pouch-like parenchyma clings more or less strongly 

 to the separating surface. 



In the elongation of the parenchyma these out-pushings differ from the 

 tan disease in which cork excrescences are concerned essentially. 



von Tubeuf ^ describes a case of the Weymuth pine very similar to that 

 on Ulmus, only no shedding of the bark strips could be observed because 

 of the smoothness of the bark. The pine was diseased and covered with 

 cushions of Xanthoria parietina. Among these lichens were found blister- 

 like processes, of which part appeared to be split and were produced by a 

 distention of the bark tissue. The resin ducts were enlarged, the deeper 

 bark parenchyma cells elongated into pouches and poor in chlorophyll. 



von Tubeuf's statement that he had produced very similar knob-like 

 processes on a branch by wrapping it with cotton wadding which was kept 

 constantly moist, warrants the assumption that, in the cases above described, 

 w^e perceive the action of a local excess of water. 



The same kind of processes as these in the bark have been observed 

 on roots also. Some years ago a serious disease of the grapevine was re- 

 ported from near Lindau". Its effects were similar to those caused by the 

 rust fungus, but it could not be proved to be of parasitic origin. The part 

 of the trunk beneath the soil and the older roots exhibited tears i to 3 

 cm. long from which protruded calluses, white at first but later turning a 

 chocolate brown. The lateral roots near these calluses died. The calluses 

 consisted of bark parenchyma cells abnormally lengthened radially and 

 scarcely connected any longer. The American varieties, scattered among 

 the diseased European vines, were found to be unaffected. As is well- 



1 V. Tubeuf, Intumescenzenbildung der Baumrinde unter Flechten. Naturw. 

 Zeitschr. f. Land- u. Forstwirtsch. 1906, p. 60. 



2 Kellermann im Jahresber. d. Sonderausschusses f. Pflanzenschutz. Arb. d. 

 Deutsch. Landw.-Ges. 1892-93. 



