Hackel showed by comparison with a rolled leaf attached to its sheath and ligule (e.g. Psamma) that such an awn as that of Bromus Alopecurus attached to its palea stands in the relation of a leaf to its sheath, the part of the palea above the insertion corresponding to the ligule, the awn itself to the lamina, and the palea below its insertion to the sheath. This view is rendered the more probable by the anatomy of the awn and by the observations of Schmid, who has shown that the awns of cereals contain chlorophyll-tissue and a vascular bundle, and have stomata, and his experiments led him to conclude that in the young condition they transpire and assimilate, and probably even contribute to the nutrition of the ripening grain. When dry and mature the awns subserve biological functions of quite another kind, and as we shall see are of importance in the distribution and sowing of the grains. (Fig. [42].)
Returning to the floral diagram, we see that the two lodicules, the three stamens and the ovary still remain to be explained. Much discussion has been held regarding the lodicules. Functionally they are said to aid in the divarication of the paleæ when the period of anthesis arrives, and the stamens and stigmatic lobes are to be exposed, by swelling and driving the valve-like paleæ apart. Morphologically they have been explained as representing the rudimentary perianth, here reduced to two minute scales, but in some exotic grasses (Bambusa, Stipa, &c.) three lodicules, or even more, are present. (Figs. [35], [36].) On the other hand they may be, and probably are, scales of the nature of minute bracteoles and of no significance to the flower itself.
| Fig. 35. Floral diagram of ordinary grass. Each pair of paleæ—i.p. inner and o.p. outer palea—encloses three stamens (s), two lodicules (l) and the ovary. st, stigmatic plumes. a, axis. | Fig. 36. Floral diagram of a
Bamboo, showing six stamens,
three inner (i.s.) and three
outer (a.s.), and three lodicules
(l) in addition to the
ovary. i.p. inner and o.p.
outer palea. a, axis. |
If this is so the flower of the grass is perfectly naked, and consists in the typical case of three stamens and one carpel. The development of the ovary lends no support to the view that there are two carpels: the stigmatic plumes are not separate styles. Nor does the fact that some grasses have six stamens lend support to the idea that the flower is derived from the trimerous type so common in Monocotyledons: other numbers may occur—e.g. as few as two (Anthoxanthum, Fig. [32]) or even one only (Uniola, Cinna, &c.) or as many as 20 or 40 in certain other exotic grasses.
Even when three stigmatic plumes are developed, as in some Bamboos, close investigation does not confirm the view that the ovary consists of more than one carpel.
We must therefore regard the flower of the grass as typically composed of one carpel and three stamens, with no perianth whatever. It is subtended by one or more bracteoles (the lodicules), and enclosed in a pair of bracteoles one higher than the other (the paleæ). The glumes are bracts of the partial inflorescence—the spikelet.
That there are some departures from this type in detail does not invalidate the importance of the fact that most grasses conform to it.
I now pass to the consideration of a grouping of our ordinary grasses according to their floral arrangements.
The student should distinctly understand that the following notes are intended to serve as an introduction to the floral characters of our grasses, and not to replace the study of the Flora. I have dealt with this section of the subject less in detail, because our best Floras give so much information that it seemed undesirable to do more than attempt to guide the reader in the recognition of the genera and principal species by means of external features easily observed by anyone with a little care. The detailed and critical examination of species, varieties and rare forms should always be done with reference to a complete Flora.