In Umbelliferæ the substitution of leaves for involucral bracts is not infrequent. It has been observed among other plants in Angelica Razoulzii, Carum carui, Daucus Carota, &c. The scales of the hop (Humulus Lupulus) not infrequently manifest this change, as do also the bracts of many amentaceous plants, e.g. in the male catkins of the walnut, the female catkins of the alder,[248] of some willows,[249] &c. The bracts of some Euphorbiaceæ, as E. pusilla, E. Lathyris, E. Cyparissias, have been observed to undergo a similar alteration.[250]
Amongst monocotyledons an analogous change occurs not unfrequently, as in some commelynaceous plants, e.g. Tradescantia, in Musa, &c.
The spathe of Arum maculatum is sometimes represented by a stalked leaf similar to that which occurs, under ordinary circumstances, in Spathiphyllum, but in which genus the spadix is more or less adherent to the leaf-like spathe.[251] In Schœnus cephalotes a similar exaggerated development of the bracts is figured by Rottboell.[252]
Phyllody in inflorescence of Conifers.—This demands passing notice by reason of the interest attaching to the morphological construction of these plants. The elongation of the axis which occurs in the female cones has been already alluded to under the head of prolification of the inflorescence. This change is frequently associated with a more or less foliaceous condition of the bracts, which, indeed, may be seen to be serially continuous, both above and below, with the ordinary leaves. The scales, too, become notched and bipartite, and show, between the lobes, the rudiment of a bud, which in a further stage becomes developed into a shoot bearing leaves. Such a change has been described by Parlatore in Abies Brunoniana, and examples may frequently be met with in the larch (Larix europæa), and specially in Cryptomeria japonica.[253] The scales of the male catkins of conifers likewise occasionally assume the appearance of leaves; this may be seen in monstrous catkins of Araucaria, as also in Podocarpeæ and Cupressineæ (Eichler).
Phyllody of the calyx.—Sepals under ordinary circumstances are so like leaves, that it is not wonderful that they are often replaced by those organs.[254] A singular instance of this has been mentioned as occurring in Cakile maritima, wherein the sepals were found by M. Fournier to be pinnatifid like the ordinary leaves of the plant.[255] The sepals of Ranunculaceæ and Rosaceæ, for example, Rosa, Geum, are particularly liable to this change.
Fig. 129.—Flower of rose, sepals replaced by five perfect leaves; axis prolonged through the flower in the form of a leafy branch.
In a species of Geranium recently examined the sepals presented themselves in the form of three-lobed leaflets; so in fuchsias and in Epilobium hirsutum the sepals occasionally are not distinguishable from ordinary leaves (fig. 130). In roses, the change in question is a very frequent accompaniment of prolification (fig. 129). In the peach also this replacement of the sepals is sometimes carried to such an extent, that five perfect, bistipulate leaves occur in the place of the calyx, but when this is the case it usually happens that the pistil is abortive.