Tin; FACTORS OF AN EPIDEMIC. 157 



epidemic was so much worse in the Southern 

 vineyards than in the more Northern ones of 

 Germany, the opinion seems to prevail that the 

 warmer ch'mates favour the insect. Further, it 

 appears that, in Italy, the vines in loose open 

 soil, provided it is equally rich in mineral food- 

 materials and offers no disadvantages as regards 

 drainage, suffer less than those in closer soils, the 

 reasons alleged being that the young roots can 

 push out more rapidly and widely, and so obtain 

 holdfasts with greater distances between them. 



Notes to Chapter XVI. 



The student may obtain further information on the 

 history of the Potato disease by consulting the following : 

 Berkeley, " Observations, Botanical and Physiological, on 

 the Potato Murrain, '^ Joiiriial of t lie Hof'ticiiltural Society, 

 Vol. I., 1846, p. 9 ; De Bary, Die Gegettwcirtig herrschende 

 Kartoffel Krmtkheit, etc., Leipzic, 1861 ; and the pages of 

 the Gardeners' Chronicle horn i860- 1900. 



For the Larch disease he should consult Hartig, Unters. 

 aus der Foist. Bota?iisc/ie/i Inst. Miinchen, B. I., 1880; 

 and Willkomm, Microscop. Feinde des Waldes., B. II., 1868. 



For Phylloxera the literature is chiefly in the Comptes 

 Rendus and other French publications since 1875, and in 

 the Reports of the U.S. Dept. of Agriculture. 



For a summary of the facts concerning the life-histories 

 of the parasites referred to above, see Frank, Krankheiten 

 der PJlanzen, and Marshall Ward, Diseases of Plants, 

 p. 59, and Timber and Some of its Diseases, London, 1889, 

 chapter X. 



Also Marshall Ward, " On some Relations between Host 

 and Parasite in certain epidemic Diseases of Plants," Proc. 

 Roy. 5<7C., Vol. XLVII., 1890, pp. 393-443; anc^ " Illustra- 



