In Cynosurus and the simpler forms of Dactylis, we find the spikelets crowded round about three quarters of the surface of the rachis, leaving the fourth quarter naked; and, finally, in Phleum, Alopecurus, Hordeum, and Anthoxanthum the spikelets cover the entire surface.
In the first (Nardus) and third examples (Cynosurus, Dactylis) where the spikelets are turned to one side, the inflorescence is said to be secund.
The next point to notice is that not every grass has so many as two fertile flowers and one barren one in its spikelet, as the Oat has. A spikelet may have one (Phleum), two (Aira) or three (Avena) or more (Poa) fertile flowers, and no barren ones or several, the number of flowers being counted by the number of pairs of pales found inside the pair of glumes. Moreover every flower is not necessarily fertile (e.g. Arrhenatherum, Holcus) and several grasses have one or more flowers in each spikelet containing stamens only—male flowers—while others may have ovaries only—female flowers. In some exotics the male and female flowers are on different parts of the same plant (Maize) or even on different plants (Gynerium), an arrangement not met with in our grasses. Accordingly, it is of importance in determining a grass to discover how many flowers the spikelet contains, and whether any are male only, or barren, &c., as well as to make out the character of its inflorescence.
In the following lists I have brought together some of the chief points with illustrative examples.
Spikelets with only one perfect flower
(without rudimentary ones).
Psamma.
Milium.
Nardus.
Alopecurus.Phleum.
Hordeum.
Agrostis.
| Psamma. Milium. Nardus. Alopecurus. | Phleum. Hordeum. Agrostis. |
And species of the rare grasses Calamagrostis, Mibora, Lepturus, Spartina, Cynodon, Gastridium, Lagurus, Polypogon, Leersia.
Spikelets with one perfect flower and one or more male or rudimentary ones.
Digraphis.
Anthoxanthum.Holcus.
Arrhenatherum.
|
Digraphis. Anthoxanthum. | Holcus. Arrhenatherum. |