A correspondent writes: The one hundred and fifty six species (or varieties, perhaps), of the Eucalyptus tree, from Australia, has, owing to its many excellent qualities for both timber and medicine, been largely planted in California some of which are even now nearly one hundred feet high, and fifteen inches in diameter, although only some twelve years old; proof beyond question of its rapid growth, and if hardy enough, would be a valuable addition to the timber of our Western prairies. The quality of hardiness however has yet to be tested, in this State, it being planted only below the line of frost as a general thing.