os = nn 
AIR-CELLS. 
about the first week of August; and when grown 
on sandy loam, it yields per acre when in flower 
10,890 lbs. of green produce, 4,9004 lbs. of dry 
produce, and 340; lbs. of nutritious matter,—and 
when in seed, 6,806} Ibs. of green produce, 3,403 
Ibs. of dry produce, and 1274 lbs. of nutritious 
matter. : 
Avra cespitosa, tufted hair-grass or hassock- 
grass—now sometimes called Deschampsia cespi- 
tosa or tufted Deschamps’-grass—delights in wet, 
clayey soils, which abound in surface water, but 
occurs in almost every variety of pasture land, and 
forms dense tufts of hard, stiff, worthless herbage, 
which farmers designate hassocks and bull-faces, 
and justly regard as a pest upon their fields. 
Though not inferior to several decidedly useful 
grasses in either the bulk of its produce or the 
proportion of its nutritious matter, it has so 
harsh and wiry a texture as to be totally unfit 
for cultivation; and it sums up nearly all its in- 
terest in the bad fame of annoying farmers with 
its ‘ hassocks,’ and being a troublesome and stub- 
born weed. Some farmers attempt to extirpate 
it, by digging up the hassocks, and filling their 
place with lime compost; some, by cutting down 
the hassocks in a series of frequent mowings ; 
and some, by shaving it clean, and depriving it 
of its early shoots in spring. But eventually the 
most profitable cure, and by far the most effec- 
tual, is the thorough draining of the land,—ac- 
companied, if the. clay be very stiff, by such 
georgic treatment as will create some porosity 
| in the soil. Avra cespitosa flowers about the 
| third week of July, and ripens toward the end of 
August ; and when growing upon clayey land, it 
| yields per acre when in seed, 10,209 lbs. of green 
produce, 3,318 Ibs. of dry produce, and 319 lbs. of 
nutritious matter. 
Aira flexuosa, zigzag hair-grass or wavy moun- 
tain hair-grass, prefers a deeper though not a 
richer soil than Festuca ovina, and naturally grows 
among furze, while Festuca ovina grows among 
| heath; yet it frequently occurs intermixed with 
that grass; and it forms a very suitable ingredi- 
ent in a mixture of artificially sown grasses, for 
the second-rate improvement of heathy and furzy 
lands. Its produce on a heathy soil is double of 
its produce on loam. It flowers in the first week 
of July, and ripens in August; and when grown 
on heathy, clayey land, it yields per acre when in 
flower 10,2093 lbs. of green produce, 3,318 lbs. of 
| dry produce, and 319 lbs. of nutritious matter,— 
and when ripe, 9,528? lbs. of green produce, 
3,573 lbs. of dry produce, and 2973 Ibs. of nutri- 
tious matter. 
The total number of species of Azra known to 
botanists is about thirty; and the most inter- 
esting of these to British agriculturists, addi- 
tional to the four we have noticed, are the follow- 
ing: Azra lavigata, smooth-sheathed hair-grass, 
indigenous on the lofty mountains of Scotland; 
Aira truncata, Pennsylvanian hair-grass, a native 
of North America, introduced to Britain in 1819; 
AIRING. 99 
Aira media, intermediate hair-grass, a native of 
the south of Europe, introduced to Britain in 
1820; Azra pulchella, pretty hair-grass, a native 
of Spain, and an annual, introduced to Britain in. 
1820; Aira caryophyllea, silvery hair-grass, an an- 
nual, and indigenous in sandy pastures in Britain ; 
Aira canescens, grey-panicled hair-grass; Adra 
precox, early-flowering hair-grass; and a newly 
discovered and unnamed species, quite recently 
introduced from Van Dieman’s Land. But only 
about eighteen of the species are retained in the 
genus by the most recent systematic botanists ; 
and several of those we have named, as well as 
some others, are assigned to newly erected genera, 
or rearranged among old genera, in classifica- 
tions founded upon minute and obscure charac- 
ters.—Sinclair’s Hortus Gramineus Woburnensis. 
—Loudon’s Encyclopedia of Plants and Hortus 
Britannicus.—Catalogue of the Highland Society’s 
Museum.—Treatise on Husbandry in Lib. of Use- 
ful Knowledge. 
AIR-CELLS or Lacuna. Cavities containing 
air, in the leaves, stems, or other parts of plants. 
In water plants, particularly in the uci, they 
are distinct and large, and consist of small and 
very regular vesicles of cellular tissue; and when 
cut open and examined by the microscope, they 
are, in many instances, seen to possess surpassing 
beauty. Their design seems to be to make the 
plants float. In terrestrial plants, or such as do 
not float, they are of more infrequent occurrence, 
much less definite in form, and of totally un- 
known use. Familiar examples of them are the 
chambers in the pith of the walnut-tree, and the 
tubes or cylindrical cavities in the stems of the 
garlic, the bamboo, and the British grasses. Their 
form in the genus Lgwisetum is not a little re- 
markable: a chief cavity occupies the centre of | 
the stem ; a series of smaller cavities occur round 
this in a circle; another series, larger than the | 
preceding, and alternating with them, occurs 
round them in a second circle ; and the whole con- 
stitute a cavitous group of very singular symmetry 
and beauty. The name air-cells, however, is not 
at all an appropriate designation ; for it suggests 
the idea of cells similar to those of the cellular 
tissue, and at the same time denotes gaps, 
spaces, and cavities of widely different form and 
character,—tubercles, cylinders, hollows, and la- 
cerations,—some wholly occupied with air, and 
others partitioned into a series of chambers. Yet 
“where spaces containing air, and communicat- 
ing with the stomata, occur in the parenchyma | 
of the leaves, as we learn from the observations || 
of M. Ad. Brongniart that they often do occur, 
as in the case of floating leaves, there the appel- 
lation of air-cells may, perhaps, be sufficiently 
appropriate.” 
AIRING. Exercising saddle, carriage, idle- 
draught, or invalid horses in the open air. When 
conducted with moderation, and adapted to the 
condition of the animals’ health and the nature 
of their feeding, it prevents swelling in the limbs, 
