an outer epidermis, and an intermediate ground tissue, apparently nearly uniform in character, from one epidermis to the other (as in Fig. 14, a to e, p. 68). A definite number of fibro-vascular cords penetrates this ground tissue. Theoretically, if this structure consist of two parts, viz. the interior carpels and the exterior "tube," some line of demarcation might be expected to be traceable; but in the majority of cases it would seem that, as neither the inner epidermis of the tube nor the outer one of the carpels are required, they are not developed at all; and so the internal tissues of the two organs become confluent and uniform, and this accounts for the fact that the dorsal cords at least are simply embedded in this common tissue. Nevertheless, in some cases there actually is a certain differentiation in the tissue, as Van Tieghem has shown in the case of Alstromeria versicolor (Fig. 30), where a yellow band of cells marks the

PSP

Fig. 29.-Receptacular tube and
calyx-limb of Cherry.

Fig. 30.-Alstromeria (after Van
Tieghem).

junction or congenital fusion of the two parts (indicated by the line in the figure).

From the preceding descriptions, it will be seen, with regard to the sources of the cords belonging to the inner whorls, that they arise by division, radial or tangential as the case may be; and then the secondary cords thus parted off are generally included within the tissue of the tube.

H

These cords of the inner whorls may be given off at the terminal point of the pedicel; that is, at the base of the flower. In this case they may all run parallel from the base to the summit of the receptacular tube; or they may branch at various heights within the tube itself, as in Prunus, described above; or, lastly, they may not arise until the summit of the ovary is reached, when they pass off and enter their respective floral organs directly. These variations occur in both free receptacular tubes as well as when coherent to ovaries.

As an example of the first case may be mentioned Alstromeria versicolor; of the second, Galanthus nivalis, or Snowdrop; and of the third, Narcissus. In Alstroemeria, all the floral appendages have their cords distinct and independent, but invaginated by the tube of parenchyma throughout (Fig. 30). In the Snowdrop, the carpellary cords are distinct, but the perianth and andrœcium are inserted in the pedicel by a single verticil of cords, which becomes double higher up. Lastly, in Narcissus, all the parts of the flower are originally inserted in the pedicel by six cords, of which three give rise by successive tangential fission to a radial series composed of the dorsal cords of the carpels, the stamens opposite to the sepals, and the sepals themselves. Similarly, the other three form the petals together with the whorl of stamens opposite to them.*

In Campanula, and to some extent in Lobelia, the cords

*Ph. Van Tieghem, to whose researches I am indebted for the above, but which I have also paralleled in other cases, represents them neatly by the following formulas, wherein () signifies vascular union, and [] the cellular union of the receptacular tube; while (d) stands for the dorsal and (m) the marginal cords of the carpels. St, signifies petaline and St. sepaline stamens.

Alstromeria-[3 S + 3 P+ 3 St,+ 3 St,+ 3 C].
Galanthus-[3 (S + St,) + 3 (P + St2) + 3 C.].
Narcissus-[3 (S+St,+ d C) +3 (P + Stp) + 3 Cm].

belonging to the petals are given off by radial chorisis from the sepaline, either quite from the base of the ovary or from about midway up the tube; they then diverge right or left at an acute angle, and, as soon as they have reached the summit of the ovary, pass up into the corolla.* As a rule, however, the petaline cords of flowers are quite distinct from the sepaline; the six or ten, common to Monocotyledons and Dicotyledons respectively, forming the fibro-vascular cylinder in the pedicel.

In all these and other cases the cords running up the receptacular tube proceed originally from the petiole, and are, so to say, even there intended for the appendages above. Normally they retain their axial character, in being arranged in a circle round the centre; abnormally an appendicular character can be revealed, by their becoming free and assuming a foliaceous aspect, as in Roses or Fuchsia, as mentioned above; so that as long as the tube is normal, i.e. a cylinder of cortical parenchyma with cords, it is of the nature of axis, and can develop extra phyllomes and even buds; but abnormally, the foliar nature, usually limited to the floral members at the summit, is extended to a greater distance lower down and the cords may now be converted into petioles, etc.

Hence it appears undesirable to call it either a calyx tube or axial; for these terms would seem to bind one to consider it permanently and in all cases as being either of one nature or the other. The term receptacular tube is therefore best, as it certainly "receives" or supports the whorls of the flowers; and Teratology clearly shows that it can be either foliar (petiolar) or axial according to circumstances.

*This reminds one of the way in which stipular appendages of Galium, etc., are supplied with cords-not by their intercalation into the common fibro-vascular cylinder of the stem, but-from a horizontal circular zone of fibres which connects the cords of the opposite leaves.

Just as the two complete vascular cylinders of two separate floral peduncles can become fused into one oval cylinder when the latter are" fasciated," so, too, would it seem that the cords belonging to the separate parts of a floral whorl, where there is no receptacular tube, can form a single united cylinder, which one then designates as the receptacular tube.

In the case of the inferior ovary, I would again emphasize the fact that the difficulty felt as to what is axial and what carpellary is entirely removed if the undifferentiated condition of the carpels be thoroughly understood. Indeed, whenever two organs are congenitally in union the epidermis of each is undeveloped, and the two mesophyls become one; so that the dorsal cords of the carpels and those proper to the axis are alike plunged into a common tissue, which, regarded as one, is neither wholly axial nor wholly carpellary.

CHAPTER XI.

THE FORMS OF FLORAL ORGANS.

THE FORM OF THE PERIANTH-GENERAL OBSERVATIONS.—It requires but a most cursory observation of flowers to notice how great is the variability in the forms of all their organs; and the questions now before us are, how these morphological characters are correlated to the one process of pollination in order to secure the fertilisation of the flower, and how this infinite diversity of form has arisen.

*

Most important differences in this respect follow from the fact of flowers being regular or irregular, and, when adapted to insects, according as the honey is easily accessible or not. Regular flowers when borne singly are almost always terminal; † and when they are arranged in racemes, etc., they either stand out erect at the ends of their pedicels so as to be readily approached at any point of their circumference, as in the Wallflower, or else they are pendulous; under which conditions, as a rule, no particular part is favoured by the

* It is usual to speak of a flower as being regular or irregular; but the term should be, strictly speaking, confined to one whorl at a time; though when the corolla is irregular, the calyx and stamens are usually somewhat irregular as well.

+ The central and terminal flowers of many plants which elsewhere bear irregular flowers are often regular, as in Horse-chestnut, Pelargonium, several of the Scrophularineæ, as Snapdragon, Linaria, Penstemon, etc.