In the July number of the Cultivator, is the substance of a paper by the President of the Massachusetts Horticultural Society, on raising new pears. He urges the importance of raising seeds for new varieties by crossing, regularly and systematically conducted, and proposes that two good varieties of summer, autumn and winter pears, should be grown in three different locations, a quarter of a mile a part, and out of the influence of other pear trees.. The Seckel and Louise Bonne de Jersey, for instance, are to be grown by themselves, and the seeds, when taken from the ripe fruit, are to be labelled, Louise Bonne fertilised by the Seckel, and the Seckel fertilised by Louise Bonne.

It is a matter of some importance to raise new varieties of fruit, which, by the same expenditure of land and labor, will yield more certain and more abundant crops, and of greater excellence than many varieties we now possess. It is desirable, therefore, that all who may wish to devote a portion of their time to this good work, should know by what means they can most certainly attain the object they have in view. I entirely coincide in the opinion that cross-breeding is that means; but I cannot so readily subscribe to the author's method of conducting the experiment - and I venture to hope that I shall be able to prove that my objections are well founded.

It is usual with the best cultivators especially to fertilise a few flowers, not to trust to crosses which may incidentally take place between varieties growing contiguous to each other, which appears to be the plan recommended. A man may botanise a summer through without meeting with a single plant which he has reason to believe to be the offspring of two parents; yet there is little doubt that many of our wild flowers can be made to intermarry with each other. In gardens, a closer relationship exists between many plants, than between the wild flowers of the fields. We have in the garden, many varieties of one species; in the woods each plant is a distinct species - and experience has proved that it is much easier to breed between varieties than between species; hence, in gardens, natural crosses not unfrequently occur. But it will be found a true saying in this, as of more important matters, that "it is well not to trust to others what we can do ourselves" - and of all helps, the wind and insects will be found most capricious, and little to be relied on.

Pollen is known to be conveyed by the wind, for miles, and bees in their wanderings, do not limit their flights to the extent of a quarter of a mile; there is, therefore, almost as great a probability that the seeds of the two trees growing side by side, would be fertilised by the pollen of others growing at a distance, as that one tree should fertilise the flowers of the other. Each blossom of the pear, moreover, is provided with its own stamens, affording pollen at the exact time when the embryo seeds are in a condition to be fertilised. I am quite at a loss to understand by what freak the pollen of the flowers of each tree is to fertilise the seeds of its neighbor, rather than its own. That some may be cross fertilised, is probable, but they will be exceptions - and in our endeavors to improve the pear, whose seedlings require so 1ong a period to arrive at maturity, in a matter so important as crossbreeding - certainty should be substituted for chance when it can so easily be done. The late Mr. Knight and the Rev. Mr. Herbert, who have probably made more experiments in cross-breeding and hybridising plants, than any other men - applied the pollen artificially, and invariably removed the stamens from the flowers to produce seed, before their pollen had arrived at maturity, because they knew that the pistil was so likely to be affected by its own stamens, that there could be no certainty as to the result of their experiments, unless they were destroyed while yet in an imperfect state.

How much less, then, must be the chances of obtaining cross-fertilised seeds, when not only the stamens are not removed, but pollen from another plant is not directly applied. By operating on a few flowers, after the manner of Knight and Herbert, we may be sure that our seeds are cross-fertilised; by trusting to the wind and insects, there can obviously be very little certainty about the matter. The author of the paper referred to being a nurseryman, I apprehend knows perfectly well what is the usual mode of proceeding in this matter, but may have considered that it was of little use recommending the practice generally, many not knowing much about the sexual organs of plants, and the mode of distinguishing them and conducting the experiment being somewhat difficult of explanation on paper, though in the field the easiest thing imaginable. I think, however, that it may be done; and as some readers of this Journal who have not hitherto bestowed much attention on the subject, may possibly be induced to take an active interest in it, a few further remarks on the object of cross-breeding, the mode of conducting the operation, and of cultivating the see 1-bearing plants, may not be devoid of use.

In all that regards reproduction, a close analogy seems to subsist between plants and animals; and he who is a successful breeder of one, may, by applying the same principles, become an equally successful improver of the other, providing he brings to bis task an equally competent knowledge of what constitutes excellence.

Both plants and animals will only breed within certain limits. As a general rule, two animals of distinct genera cannot be made to breed with each other - and it is doubted by those most likely to know, whether a truly bi-generic mule plant has yet been seen. Animals of two distinct species belonging to one genus, as the horse and the ass, are well known to breed together, and that the offspring are incapable of reproduction. So of plants; the Morello, for instance, has been made by Mr. Knigiit to breed with the common cherry, two distinct species, and the progeny were true mules, affording abundance of blossoms, but no fruit.