84 ECONOMIC IMPOETANCE OF DISEASES OF PLANTS. 



abandoned. "Whole gardens of roses have been devastated by 

 Permwspora sparsa, and nurseries of conifers have been exter- 

 minated by Hysterium pinastri, or Agaricus melleus. 



Amongst the fungi, which attack the organs of older plants 

 and cause serious losses to cultivators, are the following : the 

 well-known potato disease caused by PhytopTithora infestans; 

 the vine diseases arising from Vncinula qnralis, Plasmopara 

 viticola, and Bematophora necatrix ; many diseases of conifers 

 and other trees. As destroyers of the fruit alone may be 

 mentioned the smut-fungi of the cereal crops. 



Other cases of injurious diseases, of more or less practical 

 import, will be described in the special part of this book ; at 

 present we shall only select a few estimates of the loss result- 

 ing from them. 



In the forest of Bischoffsreut in Bavaria — a magnificent one, 

 containing spruce, fir, and beech — eighteen per cent of the 

 felled timber consisted of wood rendered useless by decay ; 

 while fifty years ago the utilizing of the so-called fungus-sponges 

 of Polyporus fomentwrius in the same forest for manufacturing 

 purposes and for tinder, was let for a small sum (see p. 74). 



Higher figures are, however, reached when we calculate the 

 injuries on vines or cereal crops. Pierce,^ in 1892, furnished 

 estimates putting the loss resulting from the Anaheim vine- 

 disease in California at ten millon dollars. The area of infected 

 land was about 25,000 acres, in great part with an original 

 value of 300 to 500 dollars per acre, but so depreciated in 

 the course of five years that it became worth not more than 

 75 to 200 dollars. 



In the Zeitschrift fiir Pfianzenkrankheitcn 1893, the inter- 

 national phytopathological commission gave, from estimates 

 mates furnished by the Prussian statistics-bureau, a review of 

 the losses in Prussia from grain-rust. Amongst other esti- 

 mates we find that in 1891 the wheat harvest of Prussia 

 reached a total of 10,574,168 doppelcentner.^ which at 22 

 marks per d.c. = £11,459,690 sterling Of this 3,316,059 d.c. or 

 £3,593,758 was depreciated by rust. The rye harvest was 

 30,505,068 d.c. at 22 marks, of which 8,208,913 d.c. 

 or £8,896,364 was depreciated by rust. Oats reached 



' The California Vine-Disease. U.S. Dept. of Agricitlttire, Btdl. S„ 1892, p. 15. 

 - Doppeloentner = 100 kilogramme. 



