The grasses most commonly affected in this manner are Dactylis glomerata!, Poa bulbosa!, Poa annua!, P. trivialis!, pratensis!, alpina!, angustifolia, and laxa, Cynosurus cristatus, Festuca nemoralis, F. ovina!, Glyceria fluitans!, Gl. aquatica, Aira alpina!, cæspitosa!, Phleum phalaroides, Lolium perenne!, Alopecurus pratensis!, Agrostis alba, Holcus mollis!
Fig. 81.—Portion of panicle of Aira vivipara and separate floret.
From an examination of the structure of viviparous grasses Von Mohl was led to the conclusion that the lower palea is to be considered as a bract, and not a perianthial leaf, because the base of the palea surrounds the stem or axis of the spikelet entirely, and both its margins cohere towards its lower extremity.[159]
A similar condition occurs not infrequently in Polygonum viviparum, and in Juncaceæ, Cyperaceæ, &c.
In the genus Allium an analogous formation of little buds or bulbils takes place in lieu of flowers; this is specially the case with A. vineale, the flowers of which are rarely seen.
Other illustrations of a similar character, where the adventitious leaf-buds are mixed in amongst the flower-buds, are cited under the head of Prolification of the Inflorescence.
Formation of buds on leaves.—The formation of little bulbs upon the surfaces or edges of leaves, forming what are called viviparous leaves, has long been familiar to botanists amongst Alliums. Professor Alexander Braun,[160] who has paid much attention to this subject, divides cases of this kind according to the position of the buds; thus, for instance, they are sometimes formed upon the upper portion of the leaf or petiole, as in many ferns, in Nymphæa guineensis, some Arads, &c. The same condition has been met with as a teratological occurrence in the leaves of Cardamine pratensis, Hyacinthus Pouzolzii, Drosera intermedia,[161] Arabis pumila, Chelidonium majus, Chirita sinensis,[162] Episcia bicolor,[163] Zamia, &c.[164] Many species of Begonia possess the power of emitting buds from the petioles and veins of the leaf; the little ramenta or scales which so plentifully beset the surface of some of these plants likewise, in some instances, pass gradually into leaves. B. phyllomaniaca, Mart., is the species best known as manifesting this tendency, but others have it also.[165]