ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 85 



Nectria ditissima.* — According to E. Hartig, a large part of 

 the diseases to wliicli forest-trees are subject, are due to the attacks of 

 this parasitic fungus. It attacks Fagus, Quercus, Corylus, Fraxinus, 

 Carpinus, Ahms glutinosa, Acer campestre and Pseudoplatanus, Tilia, 

 Frangula, Padus, and possibly also the apple. It almost always 

 enters through wounds, especially those caused by hail or by the 

 puncture of an insect, Agrilus viridis ; but in some cases lenticels 

 appear to give the opportunity. The development of the mycelium 

 takes place especially in the autumn. The portion of the bark 

 attacked assumes a black colour. The mycelium is mostly intercel- 

 lular, and from the extremities of the excessively fine hyph^ are 

 abstricted minute conidia resembling schizomycetes. These are not, 

 however, known to serve for the propagation of the fungus, but bring 

 about the rapid destruction of the cortical tissue. The medullary rays, 

 wood-parenchyma, and vessels are also attacked by the mycelium, 

 causing a brown colour in the wood to the depth of a few millimetres. 

 In damp weather, especially in September and October, the fertile 

 cushions make their appearance, producing first conidia, and then 

 small red perithecia, the result of an act of impregnation that has not 

 yet been accurately followed. 



Larch-parasite, Peziza ■Willkommi.j — E. Hartig believes that 

 the great destruction of larch-forests, which has taken place during 

 recent years in central and northern Germany and Scotland, is mainly 

 due to the attacks of this fungus. It was first described by Will- 

 komm as a Oorticium, but is a true Peziza, specifically distinct from 

 P. calicina, which is also abundant on conifers. That this is the 

 true cause of the disease known in Germany as " Krebs," was proved 

 by the writer by actual infection. Its attacks are promoted by the 

 injury inflicted on the branches by insects, by hail, and by a great 

 weight of snow. 



The mycelium lives in the cells or intercellular spaces in the 

 bark, bast, medullary rays, resin - passages, and sieve - tubes ; it 

 develops only in the autumn and spring, and spreads most 

 quickly in the direction of length of the stem or branch. When 

 the activity of the cambium commences, a layer of cork is formed 

 between the dead and living cambium and the periphery, which is 

 broken through in the autumn by the fungus ; the cause of its growth 

 being arrested in the summer is the want of water in its substratmn. 

 Connected with the formation of the cork-layer is the flow of resin 

 out of the resin-passages which have not yet been closed by it. The 

 side of the section opposite to the infected part shows also a con- 

 siderable hypertrophy. 



The fructification of the fungus has the form of small cushions, 

 which first produce conidia capable of germinating ; the ascophorous 

 hymeuium is formed only when the environment is damp, and hence 

 chiefly near the base of the stem and on the under side of the branches. 



* Unters. forstbot. Inst. Munchen, i, (ISSO) pp. 145-50. See Uot. Cen- 

 tralbl., i. (1880) p. llcJi, 

 t Ibid., pp. 33-57. 



