fusion of their respective cords will be found. If the members arise freely, as in Ranunculacea and Cruciferæ, then their cords are inserted into the axis, having arisen by radial division or lateral chorisis.

In the case of the gynandrous pistil, the stamens have their fibro-vascular cords more or less imbedded in the recep

Fig. 20.-Echium; a, side view; b, before, and c, after shedding pollen; showing

protandry.

tacular tube, or rather the common tissue resulting from the fusion of the ovary and the tube together; the anther then stands on the summit, and if there be a short or no style, but only the stigmas terminating the ovary, then the anther is in close contact with it, as in Hippuris, Orchis, etc. When there is a style, the filament may be prolonged in adhesion with it, as in most orchids possessing the so-called column. It is not

so, however, in Aristolochia, according to Van Tieghem, though often described as such.*

To summarize the above remarks, it seems clear that all adhesions between the two whorls of the perianth, to be found mostly in the Calyciflora, is an accidental occurrence due to the hypertrophied condition of the axis in forming a receptacular tube; so that the term "perigynous" is more strictly applicable than "episepalous."

Adhesions between the filaments and corolla, or calyx if the former be wanting as in Daphne, is an adaptation to insect fertilisation; whereby a more rigid position is acquired for the stamens, coupled with a gain of leverage, etc.

Lastly, adhesions between the stamens and pistil only occur where there is a receptacular tube, or "disk," as in Nymphaea; and the fusion of filaments with the style, or between anthers and stigmas, is brought about by the very close proximity of the organs when in an early and undifferentiated state.

* Duchartre, Elém. de Bot., p. 648; Henfrey, l.c., p. 125; Benth. and Hooker, Gen. Pl., vol. iii., pt. 1, p. 123; Van Tieghem, Traité de Bot., i., p. 422.

Van Tieghem's description and figure (Fig. 21) is as follows:"The styles and stigmas are abortive, and the six carpels are reduced to their ovaries. It is, then, the thickened connectives of the anthers, coherent laterally into a tube and covered above with stigmatic papillæ, which now play the part of stigmas and of the style."

To judge from Payer's figures (Organogénie, pl. 91 and pl. 109), the stigmas appear to rise from the inner side of the very short filaments, and might be interpreted as truly carpellary stigmas, but fused to the former. A further investigation of the distribution of the fibro-vascular cords should Fig. 21.—Arisbe made. Moreover, Asarum does not appear to have any- Van Tieghem). tolochia (after thing so abnormal.

CHAPTER IX.

THE CAUSE OF UNIONS.

HAVING now noticed the different kinds of unions, we may ask what has brought them about.

We have seen how progressively complex conditions can be traced from entire freedom, as in Buttercups, through forms of Cohesion, such as the gamosepalous, gamopetalous, monadelphous conditions, etc.; to cases of Adhesion, as of the perigynous and epipetalous states; and, lastly, to the adhesion of the ovary to the receptacular tube.

As stated above, these conditions are correlated with greater and progressive differentiations of the floral organs, which have been brought about by insect agencies. The above-mentioned and other terms do not, however, explain how or what the immediate influences are which induce unions of various kinds amongst the parts of flowers; but some researches of Mr. Meehan on the Coniferæ * will perhaps give us a clue. There is a well-known and a very generally prevailing feature amongst certain genera of Conifers-as of the Cupressineæ, for example-that the foliage can appear under two forms, the leaves being either free from their bases, or more or less adherent to the axis. The two forms of leaves have been recognized as specific characters in Juniperus,

On the Leaves of the Coniferæ, Proc. of the American Association for the Advancement of Science, 1869, p. 317.

Retinospora, etc.; but both kinds of foliage not infrequently appear together on the same plant; and, when this is the case, the spinescent and free leaves are borne on relatively less vigorous branches, the adherent foliage being characteristic of the more vigorous and quick-growing terminal shoots. It has been also noticed by Dr. M. T. Masters that not only do the broad and free leaves of Juniperus and Retinospora not occur on the leader shoots, but when the plant is variegated then free leaves (on the stem with arrested growth) are much more variegated than they are on the quick-growing leader shoot.* The last-mentioned observer has also noticed that the free foliage is characteristic of the younger condition of the plant, the adnate foliage that of the adult state.

The conclusions arrived at by Mr. Meehan are as follows: (1) The true leaves of Coniferæ are usually adnate with the branches. (2) Adnation is in proportion to vigour in the genus, species, or in the individuals of the same species, or branches of the same individual. (3) Many so-called distinct species of Conifera are the same, but with their leaves in various states of adnation.

Another very common form of adhesion, to which I have already alluded and which is most probably due to hypertrophy through succulency at an early stage, is fasciation.† Under this condition the fibro-vascular cylinder of at least two "axes," which would be normally separate, coalesce, and form an oval cylinder with, it may be, only a slight

*Gard. Chron., 1883, vol. xix., p. 657.

† For remarks on this phenomenon the reader is referred to Dr. Masters's Teratology. It is particularly common in herbaceous plants, as Lettuces, Asparagus, etc., and not unfrequent in Ash-trees. I observed a trailing plant of Cotoneaster growing over a rockery by the side of a stream in a garden, almost every branch of which was fasciated.

constriction indicating the union.

The medullas, cortical and epidermal layers, are also continuous throughout and common to the whole.

Now, the union of two opposite "appendages" to an axis, as in the case of connate leaves, may take place. This may be called foliar fasciation in which the fibro-vascular cords of each "leaf" are embedded in a common parenchyma, and all encased together within a common epidermis.

If we regard the receptacular tube of, say, Fuchsia and Narcissus in the same light, though adherent to the ovary like a decurrent leaf of a thistle or Sedum, I see no argument against the supposition that the tube, in such cases as these, may be regarded as the fasciated petioles of the sepaline and perianthial leaves, now adherent to the ovary within them.

A pear would seem to combine both axis and petioles, as the base of the ovaries is situated much above the commencement of the expansion of the pedicel (see Fig. 22, p. 90, and Fig. 26, p. 94, and consult text).

Each case must, however, be interpreted on its own merits; and I think there will be little difficulty about this, if we recognize the fact that both the pedicel and floral receptacle on the one hand, and the petioles or their floral equivalents on the other, can alike assume all the features of the so-called receptacular tube.

Now let us apply these principles of union through hypertrophy to flowers, and we have an interpretation according to the theory advanced in this book: that differences of floral structure depend largely upon different distributions of nutrition in the several organs; and that the irritation set up by insects themselves is one of the most potent causes of a flow of sap to certain definite places, which encourages local growths, thereby inducing these