Hence, in such plants there is a tendency to a separation of the sexes, while, from what has been before stated, it might be expected that rudiments of the male or female organs would be found, and also as a result of the operation of the law of inheritance. On the same principles it is easy to understand the occasional presence of the perfect in place of the rudimentary organs, as in Dianthus.
In some instances the assumption of a scale-like form by any organ is attended by a change in texture, the organs becoming dry and scarious, or fleshy. Moquin cites in illustration of the first phenomenon the flower of a Vicia, in which the petals were thick and fleshy, like the scales of a bulb; and of the second the leaves of a Chrysanthemum, which were replaced by small, glossy scales, like those which invest ordinary leaf-buds. Sometimes the entire flower is replaced by accumulations of small, acute, green scales. Cases of this kind, wherein the flowers of a pea and of the foxglove were replaced by collections of small ovate green scales packed one over the other till they resembled the strobile of a hop, have been already alluded to. Most of these scales are represented as having had other accumulations of scales in their axils.
Similar collections of scales may frequently be met with in the birch and in the oak, and probably represent abortive leaf-buds. Other cases of a like kind in Gentiana Amarella, where the scales are coloured, are mentioned elsewhere.
In some kinds of Campanula a similar change is not uncommon.
Formation of hairs, spines, &c.—The adventitious production of hairs is likewise frequently due to an arrested growth, in some cases arising from pressure impeding the proper development of the organ. In other cases the formation of hair seems to accompany the diminished development of some organ, as on the barren pedicels of the wig plant, Rhus Cotinus. A similar production of hair may be noticed in many cases where the development of a branch or of a flower is arrested, and this occurs with especial frequency where the arrest in growth is due to the puncture of an insect, or to the formation of a gall. In such cases the hairs are mere excrescences from the epidermis.
Prickles differ but little from hairs save in their more woody texture, but true spines or thorns are modifications either of a leaf or of a branch. Their presence seems often dependent on the soil in which the plants grow, or on other external circumstances.
They occur normally in the sepals of Paronychia serpyllifolia and other plants.
Formation of glands.—Under this name are associated a number of (generally) rudimentary organs very different in their morphological nature and significance, and also in their functions. Some are truly glandular or secreting organs, while others have no visible office. Anything like a complete account of these structures would be out of place, and reference is only made to them here on account of the occasional existence of intermediate forms, which throw light on the morphological significance of these structures. Thus, in Passiflora and Viburnum Opulus, the so-called glands on the sides of the petiole appear to represent leaflets, and are not unfrequently developed as such.
M. Dunal observed a flower of Cistus vaginatus in which some of the stamens were replaced by an hypogynous disc.[547] Moquin has seen similar instances in the flowers of a Rose, Hypericum, and Poppy.