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class Tctradyiu'iniia, and of the Umbcllàtoe and Syngcncsian tribes : wlicreas, trees and
shmbs, ferns, parasitic plauts, lilies, and aromatic plants, are most abundant in wai-m
climates ; only this is not to be understood merely of geographical climates, because, as
wc have scon, the physical climate depends upon altitude. In consequence of which,
combined with the ridges and directions of the mountains, America and Asia are much
colder iu the sænc degrees of northern latitude than liurope. American plants, vegetating
at forty-tivo degrees of northern latitude, will vegetate very well at fifty-two
degrees in Europe : the same, or nearly so, may be said of A sia ; wliich, in the iormcr
case, is perhaps owing to the iinmonsc tracts of woods and marshes covering the surface ;
and in the latter, to the more clei'atcd and mountainous situation of the country aflecting
the degree of temperature. So also Africa is much hotter under the tropics than
America ; because, in the latter, the temperature is lowered by immense chains of
mountains traversing tlic cxpiatorial regions ; whilo in the former it is increased by
means of the hot and burning sands that cover the greater part of its surface.
1095. Elevation influences the habits o f plants in various ways;—by exposing tlicm
to the wind ; to be watered by a very fresh and pure water from the melting of adjoining
snow ; and to be covered iu winter by a thick layer of snow, which protects them from
severe frosts. Hence many alpine plants become frozen during winter in tlie plains, and
in gardens which m-c naturally wanner than their native situations. In great elevations,
tlie diminution of the density of the air may also have some influence on vegetation.
Tlie rarity of the atmosphere admits a more free passage for the rays of light which,
being in consequence more active, ought to produce a more active vegetation. Experience
seems to prove this in high mountains ; and the same effect is produced in high latitudes
by the length of the day. On the other hand, vegetables require to absorb a certain
quantity of oxygen gas from the air during tho night ; and as they find less of that in
the rarefied air of the mountains, they ought to be proportionably feeble and languishing.
According to experiments made by Theodore de Saussure, plants which grow best iu
the high Alps arc those which require to absorb least oxygen during the night ; and, iu
this point of view, the shortness of the nights ncm- tho poles coiTcspond. These causes,
hoivcvcr, arc obviously very weak, compared to the powerful action of temperature.
1096. Gm ii anomafies ai-c found iu the comparative height in which the same plant
will grow ill dilfcrcnt circumstances. In countries situated under the equator, the two
sides of the mountain arc of the same temperature, which is solely determined by elevation
; but in countries distant from it, the warmest side is that towards the south ; and
the zones of plants, instead of forming lines parallel to the horizon, incline towards the
north. The reason, in both cases, is sufficiently obvious. In tho temperate zone we find
the same plants frequently on low and elevated situations ; but this is never the case
between the tropics.
1097. The habits o f aquatics are various, in regard to the depth o f water i thus, some
aquatics float always on the surface of the water, as Xémna ; while others ave cither
jiartially or wholly immersed. Such aquatics as grow in the depths of the sea are not
influenced by climate ; but such as ai*c near the surface ai’c influenced by climate, and
have thcir habitations affected by it.
The mo istu re , o r 7noff(?o/wiflim'«^,n.TturaUo vegetables, is a circumstance which hasapowcrfnl influence
on the facility with whicli plants grow in any given soil. Tho quantity of water absolutely necessary
for the nourishment of plants, varies according to thcir tissue ; some are immersed, others float on its
surface ; some grow on the margin of waters, with thcir roots always moistened or soaked in it ; others,
again, live in soil slightly humid or almost dry. Vegetables which resist extreme drought most easily
are, 1. Trees and herbs with deep roots, because they penetrate to, and derive sufficient moisture from,
some distance below the surface ; 2. Plants which, being furnished with few pores on the epidermis,
evaporate but little moisture from thcir surface, as the succulent tribo-
Thc qualitie s q fiv a te r , or the nature of the substances dissolved in it, must necessarily influence powerfully
the possibility of certain plants growing in certain places. But th e difference in this respect i.s
much less than would be imagined, because th e food of one species of plant differs very little from th at
of another. The most remarkable case is th at of salt-marshes, in which a great many vegetables will
not live, whilst a number of others thrive there better than anywhere else. Plantswhich grow in marine
marshes, and those which grow in similar grounds situated in the interior of a country, arc the same.
Other substances naturally dissolved in water appear to have much less influence on vegetation, though
the causes o fth e habitations of some plants, such as those which grow best on walls, as Peltària, and in
lime-rubbish, as Thhispi, and other Crucîferæ, may doubtless be traced to some salt (nitrate of lime,
¿tc.) or other substance peculiar to such situations.
1098. The nature o f the earth’s surface affects the habitations of vegetables in different
points of view : 1. As consisting of primitive earths, or the débris of rocks or mineral
bodies ; and, 2. As consisting of a mixture of mineral, animal, and vegetable matter.
1099. Primitive surfaces affect vegetables mechanically, according to thcir different
degrees of moveahility or tenacity. In coarse sandy surfaces plants spring up easily,
but many of them, which have large leaves or tall stems, arc as easily blown about and
destroyed. In fine, dry, sandy surfaces, plants ivith very delicate roots, as Protect aud
F ric a , prosper : a similar earth, but moist in the growing season, is suited to bulbs. On
clayey surfaces plants arc more difficult to establish ; but when established arc more permanent
; they arc generally coarse, vigorous, and perennial in thcir duration.
chctanu.
TU u /u u u uo ue soiuoie in water, are lound to be injurious to all vceetation of wh
Chatcau7ui'.7/.y. 1 íim ct-vilri,,.. Tí.,4. ---------i4 4._
“ “" f r fr"
1100. m j e d or secondarti soils include not only primitivo eartlLv or the débris of rocks
but vegeUblo matters only tlic medium ttaougl, which perfect plants obtain thefr
iood, but that food itself. In tlus view of the subject the temi soil is used in a vciT extensive
acceptation, as signifying, not only the various sorts of earth which constitute the
surtace ot the globe, but every substance whatever on which plants are foimd to vegetate
or from wluch they derive thcir nourisluneiit. The obvious division of soils in tliis ac!
ccptation of the tenn is tli.at of aquatic, tciTcstrial, and vegetable sods ; coiTc.spondiiig
to the division of aquatic, toiTcstrial, and p.arasitical plants.
noi. Aquatic soils arc such as arc either wholly or partially inundated with water
and arc fitted to produce such plants only as are denominated aquatics. Of aquatics
there avc several subdivisions according to the paiticuhu- situations they affect, or the
degrceof immersion they require. One o fth e principal subdivisions of aquatics is that
of marine plants, such as the Fiici and many of the A'igoe, which arc veiy plentiful in tbe
seas that wash the coasts of Great Britain, and arc generally attached to stones and rocks
near the shore. Some of them arc always immersed ; and others, which ai-e situated
above low water mark, are immersed and exposed to the action of the atmosphere alternately.
But none of them can be made to vegetate except in tlie waters of the sea
Another subdivision of aquatics is that of river plants, such as Chara, Potamogetón ami
iVymphæ'a, wMch occupy the bed of fresh water rivers, and vegetate in the midst of the
running stream; being for the most part wholly immersed, as well as found only in such
situations. A third subdivision of aquatics is that of;;a/«rfa/ or fe n plants, being such as
arc peculiar to lakes, marshes, and stagnant or nearly stagnant waters, but of ivhich tlie
bottom IS often tolerably clear. In such situations you find the Isoctcs lacústris
llowcnng msh, water ranimcnhis, water violet, and a variety of others -which nnifonnly
afreet such situations ; some of them being wholly immersed, and otliers immersed only
ill part.
1102. Earthy soils are such as emerge above the water and constitute the surface of the
habitable globe, that is every where covered with vcgctahle productions. Plants affectiim
siich soils, wluch comprise by far the greater part of the vcgctahle kingdom, are denominated
terrestrial, being such as vegetate upon the surface of the caith, without having
any portion immersed in water, or requiring any further moisture for their suiiport
beyond that which they derive from tlic earth and atmosphere. This division is, like the
aquatics, distributed into several subdivisions, according to the peculiar situations which
dilfcrcnt tribes affect. Some of them arc maritime, that is, growing only on the sca-
coast, or at no great distance from_ it, such as Ntátice, Glaúx, Námolus, samphire, sea-pea,
borne aro fluviatic, that is, affecting the banks of rivers, such as Zÿthram, Lycopus,
Eupatòrium. Some arc champaign, that is, affecting chiefly the [ilains, meadows, ami
(ailtivatcd fields, such as Cardáminc, Pragopôgon, Agrostémiiia. borne are dumose, that
IS, growing m liedgcs and thickets, such as the bramble. Some are raderai, that is,
growing on mbbish, such as Ncnccio viscòsus. Some arc sylvatic, that is, growing in
woods ov forests, such as Ntachys sylvàtica, Angelica sylvéstris. And, finally, some are
ulpme, that is, growing on the summits of mountains, such as Poix tdpiiia, E])ilobiimi
alpinum, and many of the mosses and lichens.
1103. Vegetable soils arc such as arc formed of vegetating or decayed plants themselves,
to some of which the seeds of certain other plants arc found to adhere, as being
the only soil fitted to thcir germination and dei'clopcmcnt. The [liants springing from
tlicm are denominated parasitical, as being plants that will vegetate neither in tho water
nor earth, bnt on certain other plants, to which they attach themselves by means of roots
that penetrate the bark, and from thc juices of which they do often, though not always,
derive thcir supjiort. This last circumstance constitutes the ground of a subdii’ision of
lairasitical plants, into such as adhere to the dead or inert jiarts of other plants (these are
termed epiphytes) ; and such as adhere to living plants, and feed on their juices.
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