Fig. 25.—Bifurcated male inflorescence, Cedrus Libani.
This subdivision of axial organs is not unfrequently the result of some injury or mutilation, thus Duval Jouve alludes to the frequency with which branched stems are produced in the various species of Equisetum, as a consequence of injuries to the main stem, but this is rather to be considered as a multiplication of parts than as a subdivision of one.
Fig. 26.—Bifurcated leaf of Lamium album, &c.
Fission of foliar organs.—Many leaves exhibit constantly the process of fission, such as the Salisburia adiantifolia, and which is due perhaps as much to the absence or relatively small proportion of cellular as compared with vascular tissue, as to absolute fission. In the same way we have laciniated leaves of the Persian lilac, Syringa persica, and Moquin mentions instances in a species of Mercurialis in which the leaves were deeply slashed. In Chenopodium Quinoa the leaves were so numerous and the clefts so deep, that the species was hardly recognisable, while on a branch of Rhus Cotinus observed by De Candolle the lobes were so narrow and so fine as to give the plant the aspect of an Umbellifer. Wigand ('Flora,' 1856, p. 706) speaks of the leaves of Dipsacus fullonum with bi-partite leaves; Moquin mentions the occurrence of a leaf of an oleander bi-lobed at the summit, so as to give the appearance of a fusion of two leaves. Steinheil has recorded an instance in Scabiosa atropurpurea in which one of the stem leaves presented the following peculiarities. It was simple below, but divided above into two equal lobes, provided each with a median nerve.[71] Steinheil has also recorded a Cerastium in which one of the leaves was provided with two midribs; above this leaf was a group of ternate leaves. I have seen similar instances in the common Elm, Ulmus campestris, and also in the common nettle, Urtica dioica, the leaves of which latter thus resembled those of Urtica biloba, which are habitually bilobed at the summit. M. Clos[72] mentions an instance where the terminal leaf and first bract of Orchis sambucina were divided into two segments. The same author also mentions the leaves of Anemiopsis californica, which were divided in their upper halves each into two lobes—also leaves of a lentil springing from a fasciated stem and completely divided into two segments, but with only a single bud in the axil. The axillary branches in like manner showed traces of cleavage. Fig. 26 represents a case of this kind in Lamium album, conjoined with suppression of the flowers on one side of the stem. I have also in my herbarium a leaf of Arum maculatum, with a stalk single at the base, but dividing into two separate stalks, each bearing a hastate lamina, the form of which is so perfect that were it not from the venation of the sheath it would be considered that there was here a union of two leaves rather than a bifurcation of one. A garden Pelargonium presented the same appearance.
