BOOK V. 
GEOGRAPHY. 
475 
2. Marine plants, also called Thalassiophytes by M. Lamou- 
roux, which live either plunged in salt water or floating on 
its surface. These plants are distributed over the bottom of 
the sea or of salt water, in proportion to the degree of salt- 
ness of the water, the usual degree of its agitation, the con- 
tinuity or intermittence of their immersion, the tenacity of 
the soil, and perhaps also the intensity of the light. 
3. Aquatic plants, living plunged in fresh water, either 
entirely immerged, as Confervas ; or floating on its surface, as 
Stratiotes ; or fixed in the soil by their roots, with the foliage 
in the water, as several kinds of Potamogeton ; or rooted in 
the soil, and either floating on the surface, as Nymphaea; 
or rising above it, as Alisma plantago. This last division is 
very near the following class. 
4. Plants of fresh water marshes, and of very wet places, 
among which it is chiefly necessary to distinguish those of 
bogs, of marshy meadows, and of the banks of running 
streams ; and, finally, those of places inundated in winter, but 
more or less dried up during the summer. 
5. Plants of meadows and pastures, in the study of which 
it is requisite to distinguish those that by their natural or 
artificial association form the turf of the meadow, and those 
others which grow mixed together with the greatest facility. 
6. Plants of cultivated soil. This class has been entirely 
produced by the agency of man : the plants which grow in 
cultivated land are those which, in a wild state, preferred 
light substantial soils : many have been transported from one 
country to another with the seeds of other cultivated plants. 
Those individuals of the same species, which are found in 
fields, vineyards, and gardens, are often different in some 
respects according to the peculiar manner in which they have 
been cultivated. 
7. The plants oj rocks ; these pass by insensible gradations 
to those of walls, rocky and stony places, and even of gravel ; 
and the latter soil, as its fragments diminish in size, conduct 
us by degrees to the following class. Rock plants offer some 
remarkable singularities depending upon the nature of the 
rock. 
8. The plants of sands, or of very barren soil ; in the classi- 
