Useful grasses which are increased are Lolium perenne and Alopecurus pratensis, and among those of less value Avena favescens, Dactylis glomerata and Poa pratensis.
The last three forms grow only on the genera Aira, Agrostis and Poa respectively.
Several species of the north temperate zone, such as Poa nemoralis, P. pratensis, Festuca ovina, F.
During spring, autumn, and winter in particular, the blue-grass (Poa compressa and Poa pratensis) spreads a mat, green, thick, fine and soft, over much of the country, and it is a good winter pasture; about the middle of June it blooms, and, owing to the hue of its seed vessels, gives the landscape a bluish hue.
Some species, such as Poa stricta, are known only in this viviparous condition; others, like our British species Festuca ovina, and Poa alpina, become viviparous under the special climatic. conditions.
Hygrophytes.Plants which are sub-evergreen or evergreen but it scierophyllous, and which live in moist soils; e.g., Lastraea lix-mas, Poa pratensis, Carex ovalis, Plantago lanceolala, and ihillaea Millefolium.