That these are constantly appearing, is a matter of common observation; but the manner of their production has given rise to much diversity of opinion. The theory that they are the results of replanting, from the seeds of successive generations of the same tree, is called the Van Mons' theory, after Dr. Van Mons, of Belgium, who devoted many years of close study and application to the improvement of fruit, especially of pears, by this method. His directions may be briefly summed up as follows. Plant seeds from any good variety of fruit; let those seedlings stand without grafting, until they bear. Take the first fruit from the best of those seedlings, and plant it and produce other seedlings, and so on. The peach and plum are said to reach a high state of excellence in the third generation, while the pear requires the fifth. Seeds from old trees are said to have a great tendency to return to their wild origin, while those of young, improving trees will more generally produce a better fruit. The seeds from a graft from a young tree does not produce a better than itself. The succession must be of seedlings. This theory requires long practice, and is exposed to interruptions by the crosses that will necessarily occur between different trees in blossom. And we have in so many cases had a fruit of great perfection arise from a single planting of seed from some known variety, that we must conclude the improvement to be produced by some other principle than that of the Van Mons' theory. The evidence is in favor of the opinion that new varieties of fruit arise from cross-fertilization in the blossoms of different kinds, and that the improvement of the qualities of any given variety is the result of cultivation. Some of the best plums we have are known to have been the product of fertilizing the blossoms of one tree from the pollen of another; this is constantly taking place with our fruits, and is consequent upon our mixed orchards. Let this be attended to artificially, by covering branches with gauze, to prevent the fertilization by bees and winds, and make the cross between any two varieties you choose, and the results may prove highly beneficial. The amateur cultivator may render essential service to pomology by this practice. We know that all our choice fruits have come from those not fit for use. It is not improved cultivation of the old, barely, but the production of new varieties. The subject of further improvement, therefore, demands careful study and practice. The seeds of established varieties, planted at once without drying, will often reproduce the same. We are not certain but they generally would, if not affected by blossoms of contiguous trees. NURSERY.