If we enquire further why the _Phylloxera_ 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 climates 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," _Journal of the Horticultural Society_, Vol. I., 1846, p. 9; De Bary, _Die Gegenwärtig herrschende Kartoffel Krankheit_, etc., Leipzic, 1861; and the pages of the _Gardeners' Chronicle_ from 1860-1900. For the Larch disease he should consult Hartig, _Unters. aus der Foist. Botanischen Inst. München_, 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 Pflanzen_, 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. Soc._, Vol. XLVII., 1890, pp. 393-443; and "Illustrations of the Structure and Life-history of Phytophthora infestans," _Quart. Journ. Microsc. Soc._, Vol. XXVII., 1887, p. 413; also Marshall Ward, "Researches on the Life-history of Hemileia vastratrix," _Journ. Linn. Soc._, Vol. XIX., 1882, p. 299; and "On the Morphology of Hemileia vastatrix," _Quart. Journ. Microsc. Soc._, 1881, Vol. XXI., p. 1. CHAPTER XVII. REMEDIAL MEASURES. _Preventible diseases--The principles of therapeutics--Powders and their application--Spraying with liquids--Nature of chemicals employed--Employment of epidemics and natural checks--The struggle for existence._