There is no evidence concerning the question, as to whether during the periods mentioned apples were cultivated or only collected in the wild state. The very large numbers which are found, have induced some writers to believe in their culture, but then there is no reason why they should not have been collected in quantity from wild shrubs. The main fact is that the apple was not a uniform species in prehistoric times but showed even then at least some amount of variability. At the present day the wild apples are very rich in elementary species. Those of Versailles are not the same as those of Belgium, and still others are growing in England and in Germany. The botanical differences derived from the blossoms and the leaves are slight, but the flavor, size and shape of the fruits diverge widely. Two opinions have been advanced to explain this high degree of variability, but [76] neither of them conveys a real explanation; their aim is chiefly to support different views as to the causes of variability, and the origin of elementary species at large. One opinion, advocated by De Candolle, Darwin and others, claims that the varieties owe their origin to the direct influence of cultivation, and that the corresponding forms found in the wild state, are not at all original, but have escaped from cultivation and apparently become wild. Of course this possibility cannot be denied, at least in any single instance, but it seems too sweeping an assertion to make for the whole range of observed forms. The alternative theory is that of van Mons, the Belgian originator of commercial varieties of apples, who has published his experiments in a large work called "Arbres fruitiers ou Pomonomie belge." Most of the more remarkable apples of the first half of the last century were produced by van Mons, but his greatest merit is not the direct production of a number of good varieties, but the foundation of the method, by which new varieties may be obtained and improved.