We take it, then, that there is a primordial oneness of sex, as Plato long since argued, and in that sense we agree with Dr. Spruce. We are constantly meeting in plants with traces of this essential unity of sex. We can see it in the development of all flowers; we meet with it frequently in the structural changes from one sex to the other, and to which we have already drawn attention. If we find the same organ bearing, at the same time, on one side pollen and on the other side ovules—a by no means unusual occurrence-it is difficult to conceive that there can be so great an intrinsic difference between the sexes as is usually admitted. If we find the pistil producing pollen, and the stamens forming ovules-as happens not unfrequently in the common stonecrop and in the wallflower- -our belief in the absolute diversity of the two sexes becomes less implicit. If we meet with ovules bearing pollen in their interior, as has now been seen in species of passion-flower by Mr. J. A. Salter, and by the writer in a rose, our faith in the duality of sex becomes well nigh uprooted. In face of such evidence is it not reasonable to suppose that as sexual characteristics of any kind are themselves secondary in point of development, and individual, not specific, so the dual nature of the sexual principle, so conspicuous in the adult organism, is a later development or evolution from an originally homogeneous unity? The old tradition of the development of Eve from the rib of our forefather Adam may not after all be so purely mythical an assertion. What Milton said of the spirits may, if we exclude the notion of volition, be properly applied to plants :—

"Spirits, when they please,

Can either sex assume, or both."

It remains now to enquire what are the causes which disturb the equilibrium in the first instance, and to ascertain what are the special circumstances which favour the development of one sex at the expense of the other.

With reference to the first point, it would appear that although very slight causes are sometimes sufficient to deflect the balance, yet at others, and those more frequent, much more violent changes are powerless to bring about such a result.

Allusion has been already made to a seedling Papaw, the produce of American seed developing hermaphrodite flowers when grown on the shores of the Mediterranean, and the changed conditions have been assumed to be sufficient to account for the phenomenon. On the other hand we have seen a male plant of the Papaw, cultivated for years in the Oxford Botanic Garden, suddenly produce bisexual flowers without obvious change of condition; and numerous parallel changes are familiar to all observers. Sometimes in these cases

it is not made sufficiently clear whether ripe fruit only, or ripe fruit containing ripe seeds capable of germinating, are developed a very important element to be considered, as the fruit may often ripen and develop only imperfect seed or none at all.

The structural changes hitherto effected as a consequence of man's interference, either intentionally or of necessity, are relatively slight. Consider, for instance, the artificial conditions under which plants are transplanted, pruned, grown, fed in gardens, and then contrast the rare instances in which any absolute or essential changes in structure (not merely of degree of development, more or less) occur. Important structural changes of a relatively permanent character appear, as a rule, to be brought about very slowly and gradually.

As regards functional activity, however, the case is very different. Very slight alterations will often immediately and profoundly modify the fertility of a given flower and the vigour of its seedlings. Cases are recorded wherein a flower ordinarily sterile, when fertilised by its own pollen, has developed perfect fruit and seeds when grafted on to some other species. Cultivation, climatic changes, diseases, injuries, all have a tendency to influence for good or ill the reproductive functions of plants, even though the change in circumstances be apparently slight, and the structural alteration consequent on them absolutely inappreciable.

We have already cited instances where altered climatal conditions, as the transfer of a plant from Europe to America, have, on the other hand, induced changes in the sexual organisation of the plant. There are several cases cited where a species growing within certain latitudes is of one sex chiefly, while the same species growing in other latitudes developes mainly flowers of the opposite sex. Instances of a similar character are related in reference to moisture. A willow growing in a very wet locality has been known to produce female flowers only, while in a dry place male catkins only were produced. In the case of some Begonias, which, under ordinary circumstances, produce separate male and female flowers on the same plant, Mr. Anderson Henry has succeeded in inducing the formation of female flowers only by removing two out of the three stigmatic lobes, and fertilising the remaining one. All the plants, four or five in number, which have resulted from this cross, have produced female flowers only. Mr. Henry has repeated the experiment with the same result. Such observations as these need confirmation and extension; and from the ease with which they may be made, and their importance, may be commended to the special notice of amateurs. It is obvious also that in the case of ordinarily

hermaphrodite flowers the time at which an alteration of the "environment occurs must be taken into consideration. As a rule, the stamens are developed before the pistil; hence if some check to growth accrue, it may occur before the formation of the pistil, when a staminiferous flower would result. Or, again, the circumstances inducing an arrest of growth at the period when the stamens are forming may subsequently change, and the pistil be regularly formed, though the stamens remain undeveloped or abortive.

That the precise period at which growth and development take place is an element of great importance in such matters, is one which no physiologist is likely to dispute. Not to mention cases in the animal kingdom, it is sufficient to say that the conformation of flowers produced out of their accustomed season is very often more or less deranged; their position is often different, their form changed, the number and arrangement of their parts altered. Of course the reproductive organs undergo corresponding changes. The flowers of apples or pears which are occasionally produced on the so-called “midsummer shoots" have perfect stamens, but rarely perfect pistils. Under ordinary circumstances, the flowers we have mentioned are developed in autumn, on short stunted branches or spurs, and remain quiescent till the following spring; but in the cases under consideration an imperfect flower is formed within a few weeks, at the end of a long, weakly shoot, also of rapid growth. There is nothing surprising in this; it is just what might be expected, and it furnishes an illustration of our argument that the period at which certain changes occur is an element of cardinal importance in the determination of the nature of those changes. Baillon records having met with an hermaphrodite flower in June on the common hazel. It would be sufficiently extraordinary to meet with such a flower at any time, but it seems more consistent to meet with such a flower in summer rather than in winter, the normal period of flowering.

The bearing that this part of our subject has on practical gardening is obvious, and particularly in the case of forcing. Practical gardeners know well that in forcing vines, pines, strawberries, cherries, cucumbers, or indeed any plant which is required to produce its flowers and fruit out of due season, they cannot be too careful in the timely regulation and adjustment of the heat and moisture at their disposal. Want of care, or deficient judgment, will defeat the object aimed at, and a crop of leaves only, or sterile “blind" flowers, or flowers which refuse to "set," will be the consequence. The anatomist knows the structural reasons for this; the physiologist speculates on the causes which put the structures into action; the practical man, taught by experience, knows how to avail himself both of the one and

the other-if not to make the machine, at least to set it going, and regulate its action according to his wishes.

In this place we may appropriately call attention to the opinions of Mr. Meehan on the sexuality of plants, and which demand attention as the opinions of a practised cultivator, a good observer, and a shrewd reasoner.* As the result of his observations, he comes to the conclusion that in plants a high degree of vigour produces the female sex, while a less robust constitution is sufficient for the development of the pollen. In this manner the alternation sometimes observed in unisexual plants may be accounted for. A plant producing fruit, and more particularly ripe seed, for a succession of years, becomes more or less exhausted, and during the period when it is recruiting its energies it forms male flowers only. Mr. Meehan bases his theory on the relative position of the flowers of the two sexes, showing that the female flowers are, as a rule, placed on the strongest axial parts, the male ones on the weakest. As a consequence of this, the female flowers are so placed as to receive the direct flow of the nutrient fluid, while the male flowers often derive their supplies from collateral, or less direct sources, and in smaller quantities. He further goes on to show that the invigorating effects of climate, of manuring, &c., tend more particularly to the development of the female rather than to that of the male flower.

Apart from ascertained facts, it seems reasonable to suppose that a less degree of vital energy would be required for the staminate flowers, whose functions are much sooner fulfilled, than for the pistillate flowers, whose office of forming, protecting, ripening the pistil, and more especially its contents (the ripe seed), naturally occupies so much longer a period, and involves so much larger a demand on the resources of the plant. There are several facts which lend colour to this theory. In America, strawberry-blossoms are frequently unisexual. In this country, also, some varieties are apt to produce "blind," i.e. sterile flowers. The same thing happens in vines, and indeed in many other plants. Spruce and Meehan, as we have seen, would consider this tendency to produce unisexual flowers as an evidence of progress; and so indeed it may be, on the principle of division of labour. The gardener, however, looks upon the occurrence in quite a different light, and does his best to rid himself of such undesirable plants. But if the advantage accruing from division of labour, and specially from the operation of cross fertilisation, were fully recognised by him, he should rather promote than discourage such a tendency, and counteract the sterility by the artificial employment of pollen from some

* Cited in "Gardener's Chronicle," 1870, p. 243.

other plant or variety. In this manner, too, he would counteract that weakness of constitution, the result of continual in-and-in breeding, and which is so apparent in many of the higher bred flowers and vegetables of the present day, and which leaves them an easy prey to disease and parasitic fungi. At any rate, we owe to the observation of practical gardeners the establishment of the fact that a relatively high temperature is most conducive to the formation of stamens in the case of strawberries, a low temperature to that of pistils. So again, in the case of vines, it has been observed that a high temperature conduces specially to the formation of tendrils, a low one to that of fertile flowers. It is probable, however, that varying conditions of moisture may have as much effect in this way as the mere variation of temperature.

That parasitic fungi should determine the formation of stamens seems at first sight sufficiently remarkable. Nevertheless such is the opinion held by M. Cornu, in France, and it was independently brought before the notice of the British Association at Exeter, by Miss Becker. Moreover, the notion receives the assent of the veteran mycologist, the Rev. M. J. Berkeley, than whom none more competent to express an opinion on such a subject. The facts are as follows:-The common Lychnis of our hedges, Lychnis diurna, has unisexual and diœcious flowers; but when affected by a parasitic fungus, the flowers, which should be pistillate only, develop stamens also. This is attributed by Miss Becker to the fact that the fungus (Ustilago antherarum), although able to penetrate the plant, can only fructify in the anthers, and consequently it becomes the determining cause of the production of the stamens in the normally female flower. We have not all the evidence before us, on which account we find it difficult to understand how the presence of the fungus in the anthers should be taken as a proof that they (the anthers) were called into development by the fungus. That other flowers on the same plant unaffected with fungus should have pistils only and no stamens, is surely not to be taken as a proof that parasitic fungi can cause the development of stamens. The origin of sexual differences, and the power of inducing in animals the appearance of one or other at will, have from the oldest times exercised the thoughts of philosophers. As we have seen, the solution of the problem is not only of the highest interest as a matter of science, but also as regards the direct material welfare of mankind. Without intending any disparagement to the devotees of the sister science of zoology, we may yet affirm confidently that the botanists and gardeners between them have so far advanced considerably beyond their confrères in the unravelling of this, by no means the least, of the mysteries of life.