Page:Popular Science Monthly Volume 25.djvu/408

396  (b) Color and general condition of the bark. (c) Character of the new growth. (d) Condition of the fruit. (e) Presence of parasites.

We can not hope to correctly determine the nature of diseases by seeking new light upon strictly botanical grounds alone—e. g., by assuming that they originate more or less directly in fungoid growths. Nor can we hope to get at the origin and cure of these disorders from a purely chemical stand-point. The two lines of inquiry must be followed together until they merge in one harmonious result. In such manner alone may we hope in the future to solve the difficult problems now awaiting the patient student, to whom they will bring abundant reward.

These thoughts are offered as a mere outline of the direction which such considerations in vegetable pathology are now taking, and of the form they have already assumed.



NIMALS and plants are fitted by their organization to adapt themselves to many changes of place and vicissitudes of climate. Most of the domestic plants that are cultivated in the north originated in southern regions. The trees of the orange family were not cultivated in Italy in Pliny's time. The citron was not raised there with success till the third century; and lemons and oranges, which now grow in Southern Tyrol, not till later. The mulberry, which has now made its way to Norway, likewise did not flourish in Italy when Pliny wrote. Juicy peaches were not grown in Greece in the time of Aristotle, and even in Rhodes the blossoms only developed into a thin, woody fruit; but the peach-tree, bearing choice fruit, is now common through all France, and in the gardens of Central Germany. Chestnuts, originally at home only in warmer Asia, are now equally so in Italy and Western Germany. Some plants, notably the cereals, have enjoyed a very extensive diffusion in the course of centuries, and are now cultivated in nearly every part of the habitable earth. Our domestic animals, which mostly came from Asia, have gone with man to all the quarters of the world; and it is worthy of note that it is just those cereals and domestic animals that have proved themselves most useful to man, and are essential to civilized life, that preeminently possess the faculty of adapting themselves to all climates, and of producing the most diversified varieties.

The power of adaptation to climates appears to be most highly 