[As our readers know, much attention has been given of late years to the subject of cross-fertilization of flowers by insect and other agencies. It is understood that many plants are unable to fertilize themselves, and that others which can do so, are more easily fertilized by these outside agencies than by their own act. A difference of opinion has grown out of these facts. Mr. Darwin, Dr. Gray, and others believe that cross-fertilization is a benefit to the plant or its race, and that the arrangements for cross-fertilization were expressly designed for the accomplishment of this good end. The advocates of this view had the advantage of novelty and plausibility, and for a while the ground seemed indisputable; others following, failed to see " the good results from cross-fertilization, found a great deal more self-fertilization among flowers than the other party was at one time prepared to grant, and discovered a great many risks and disadvantages to plants dependent on insect or other aid. Amongst these is the Rev. Geo. Henslow, who about a year ago published an elaborate paper on this logical question. This paper induced a lengthy review in Silliman's Journal, from the pen of Dr. Gray, which has been copied into the Botanical Gazette, and probably other papers in this country.

Prof. Henslow sent the following reply to Silliman's Journal, which the editor, Dr. Gray, though under no obligation to do so, kindly promised to insert. Subsequently an abstract of Dr. Gray's criticism appeared in the London Gardener's Chronicle, and Prof. Henslow justly apprehending that the reply would be better understood if immediately following the criticism, sent a copy of the reply, which was published in the Gardener's Chronicle, the following week. Dr. Gray now declines to publish in Silliman's Journal Prof. Henslow's reply.

If the Gardener's Chronicle were read by the same persons in this country who read Silliman's Journal, Botanical Gazette, and so forth, it would, of course, be a waste of space to reprint in Silliman's Journal. Dr. Masters did not think they were the same, or he would not have reproduced Dr. Gray's remarks in the Gardener's Chronicle; nor do we think so, and therefore, as an act of justice to a distinguished foreign scientist, we give space for the reply in the country where the criticism was made. - Ed. G. M].

"Although the Professor at first calls my essay 'unconvincing,' yet at the close of his remarks he appears to be convinced on one, and that, too, the most important point: ' Without acceding to his general proposition, we are much disposed to agree with the author in this essay as respects some of them (i. e., weeds), that aptitude for self-fertilization may have given them the advantage which has determined their wide dispersion.' This, however, at once admits that by their dispersion and by the maintaining their existence, self-fertilizing plants have proved themselves to be the best fitted to survive in the natural struggle for life. This is the sum and substance of my argument, and it necessarily involves the acceptance of the converse proposition, that plants dependent upon insects are least fitted to be dispersed and to survive. I admit to the full that all conspicuous flowers are more or less adapted to insect agency, but I demur to the expression that such flowers are ' benefited' by intercrossing. Such a term assumes self-fertiliza-tion to be the standard for comparison. But as their normal condition requires insects and crossing for full physiological effects, the results of intercrossing should be taken as the standard.

Then it would be correct to say that such plants are not benefited by self-fertilization, for their standard is often lowered, as Darwin has shown abundantly. On the other hand, with plants habitually self-fertilized, their standard is the result of self-fertilization. Now these, as Darwin, has shown with Canna, garden pea, some cleis-togamous flowers, etc., are just as indifferent to crossing, for their standard is similarly lowered by the process. But further, while the latter are not benefited by crossing, the former may be actually benefited by self-fertilization, as Darwin has proved with Hero, white Mimulus, Dianthus, etc., which, having re-acquired the power of self-fertilization, at once pass under the category of self-fertilizing flowers. Hence, coete-ris paribus, the balance must be in favor of self-fertilization. This is the logical inference which has to be refuted, if it be possible to do so. But we may proceed further. Darwin has shown that certain plants which are adapted to insects only acquire their fullest fertility when crossed with distinct stocks.

DIANTHUS CHINENSIS LACINATUS.

DIANTHUS CHINENSIS LACINATUS.

Hence the ordinary crossing of plants growing in the same soil is not perfect; so that the real alternative lies between a constant intercrossing between stocks of widely sundered localities, or else self-fertilization. The former in nature is out of the question, hence the latter is preferable, as their propaga-tive powers are enormous, and far beyond what is absolutely required to maintain their existence. Professor Gray, in speaking of the benefits of crossing, says: ' We do not doubt that sexual reproduction contributes something to the well-being of the species,' (apart from that to the individual?) 'besides facilitating its dispersion;' ' an occasional cross suffices to secure the benefit of intercrossing, whatever that may be.' I have more than once protested against the use of vague expressions, such as the words I have italicised; for they are misleading and valueless in argument. Unless it be distinctly stated what the benefit is supposed to be, and wherein I may have denied such to accrue to the plant, I can only refuse to reply. In my* paper I consider one 'end' of plant life as alone legitimately recognizable, namely, propagation.

All other so-called ' benefits' I maintain have not been proved to be such at all, and are merely subjective impressions; while all botanists admit that self-fertilization is by far the best method for securing rapid and abundant propagation. The plants alluded to, excepting Gaura parviflora, were upon the authority of others. That this species should ' open its flowers freely and bear rose-colored petals' in America, entirely confirms my statement, that flowers adapted to insects in one country or in one season may be self-fertilizing elsewhere, and vice versa, and that inconspicuous self-fertilizing forms (species) are simply reduced from their conspicuous allies. Though the many* flowers of Gaura which I examined at Kew were cleistogamous, it is just what I expected to hear, that they open in their native country. Professor A. Gray asks me if I ever asked myself the question, 'Why sexes are separate in animals ?' I reply by taking the liberty of an American, in asking him if he ever thought why they are retained in one and the same animal in many cases ? If my paper was ' unconvincing ' to the Professor, I fear, though I thank him much for it, I cannot say otherwise for his kindly criticism".