The chemical qualities, odours, and tissues of plants are often modified by a change which seems to us slight. The Hemlock is said not to yield conicine in Scotland. The root of the _Aconitum napellus_ becomes innocuous in frigid climates. The medicinal properties of the Digitalis are easily affected by culture. The Rhubarb flourishes in England, but does not produce the medicinal substance which makes the plant so valuable in Chinese Tartary. As the _Pistacia lentiscus_ grows abundantly in the South of France, the climate must suit it, but it yields no mastic. The _Laurus sassafras_ in Europe loses the odour proper to it in North America.[665] Many similar facts could be given, and they are remarkable because it might have been thought that definite chemical compounds would have been little liable to change either in quality or quantity. The wood of the American Locust-tree (_Robinia_) when grown in England is nearly worthless, as is that of the Oak-tree when grown at the Cape of Good Hope.[666] Hemp and flax, as I hear from Dr. Falconer, flourish and yield plenty of seed on the plains of India, but their fibres are brittle {275} and useless. Hemp, on the other hand, fails to produce in England that resinous matter which is so largely used in India as an intoxicating drug. The fruit of the Melon is greatly influenced by slight differences in culture and climate. Hence it is generally a better plan, according to Naudin, to improve an old kind than to introduce a new one into any locality. The seed of the Persian Melon produces near Paris fruit inferior to the poorest market kinds, but at Bordeaux yields delicious fruit.[667] Seed is annually brought from Thibet to Kashmir,[668] and produces fruit weighing from four to ten pounds, but plants raised from seed saved in Kashmir next year give fruit weighing only from two to three pounds. It is well known that American varieties of the Apple produce in their native land magnificent and brightly-coloured fruit, but in England of poor quality and a dull colour. In Hungary there are many varieties of the Kidney-bean, remarkable for the beauty of their seeds, but the Rev. M. J. Berkeley[669] found that their beauty could hardly ever be preserved in England, and in some cases the colour was greatly changed. We have seen in the ninth chapter, with respect to wheat, what a remarkable effect transportal from the North to the South of France, and reversely, produced on the weight of the grain.