Fig. 79.—Spikelets of Willedenovia, composed entirely of scales to the exclusion of flowers.
Fig. 80.—Rose Willow, Salix, sp.
Here, also, may be mentioned the curious aggregations of scales which occur in some grasses, in Restiaceæ, Juncaceæ, and other orders, in which the inflorescence is made up of collections of scales or bracts with no trace of floral structure. Fig. 79 shows this in a species of Willdenovia, and a very good example is figured in a bamboo, Pseudostachyum polymorphum, by General Munro.[156]
"Rose willows" (fig. 80) owe their peculiar appearance to a similar cause, the scales of the catkin being here replaced by closely crowded leaves. These aggregations of scales or leaves are not confined to the inflorescence, but may be found in other parts of the plant, and may be frequently met with in the willow, birch, oak, &c., generally as the result of insect puncture. On the other hand, the production of leaves or leaf-buds in place of flowers is, as is well known, generally the consequence of an excess of nutrition, and of the continuance rather than of the arrest of vegetative development.[157] It has even been asserted that a flower-bud may be transformed into a leaf-bud by removing the pistil at a very early stage of development, but this statement requires further confirmation.[158]
Viviparous plants.—The spikelets of certain grasses are frequently found with some of their constituent parts completely replaced by leaves, like those of the stem, while the true flowers are usually entirely absent. A shoot, in fact, is formed in place of a series of flowers. In these cases it generally happens that the outermost glumes are changed, sometimes, however, even the outer and inner paleæ are wholly unchanged, while there is no trace of squamulæ or of stamens and pistils within them, but in their place is a small shoot with miniature leaves arranged in the ordinary manner.