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TEEDIA. 
the bottom part of the youngest shoots; or, best 
of all, from rootings of the shoots, laid upon the 
ground, and covered with a little mould. 
TECTONA. See Teax-Woop. 
TEDDING. See Haymaxine. 
TEEDIA. A small genus of ornamental, her- 
baceous, South-African plants, of the figwort 
family. Two species, the shining and the pu- 
bescent, both purple-flowered biennials of about 
two feet in height, the former blooming from 
April till July, and the latter from May till 
October, have been introduced to Britain; and 
they love a soil of peaty loam, and are propa- 
gated from cuttings. 
TEESDALIA. A small genus of nantdeotnre 
white-flowered, hardy, annual plants, of the cru- 
ciferous order. The naked stalked or irregular 
species, 7’. nudicaulis, grows wild in the pastures 
of some parts of Britain. Its root is slender and 
tapering ; its stems rise in groups from one root, 
and are erect or spreading, and about 6 inches 
high,—the central one quite straight and always 
naked; its leaves are numerous, and spread on 
the ground, and are partly entire but chiefly 
pinnatifid; and its flowers grow in small 
corymbs, and have unequal petals, and naturally 
bloom from May till July.—The regular species, 
| 1. regularis, was introduced from the South of 
Kurope in 1824; and is smaller than the preced- 
| ing; and blooms from February till May.—Both 
Species thrive in any common soil, and are very 
suitable for rock-work, and need only to be once 
sown, and will afterwards propagate themselves. 
TEETH. The teeth of most of the higher or- 
ders of mammals—particularly those of man, of 
the quadrumana, of the carnivora, of the pachy- 
dermata, and of the hornless ruminantia—not- 
withstanding great and signal differences in the 
chief groups or genera, possess certain important 
common characters of both classification and 
composition,—or, in every case, comprise inci- 
sors, cuspidates, and molars, and consist of ena- 
mel, ivory, and osteous cement. They have dif- 
ferent forms and arrangements and relative 
numbers in different genera, to suit to a nicety 
the special wants and feeding-habits of each ani- 
mal; yet, in all instances, though more or less 
vigorously according to the saliency of their 
points and the refractoriness of the substances 
on which they operate, the incisors cut or nip, 
the cuspidates tear or lacerate, and the molars 
grind or bruise or pulverize. The three classes, 
as they exist in the horse, may be taken as a 
familiar specimen, and bear the popular names 
of nippers, tushes, and grinders, and have been 
described in our article Acr or Animas. The 
enamel, the ivory, and the osteous cement, ag- 
guepately adapt the teeth to withstand the attri- 
tion of eating, the chemical action of substances 
incidentally lodged in the interstices, the action 
of the atmosphere, and the diversity of organic 
forces within the exposed and the unexposed 
parts of the teeth; and they are differently pro- 
TEETH. 413 
portioned to one another, not only in the teeth 
of different species of animals, but in the different 
classes of the teeth of the same species, and in the 
different parts of the same tooth. The ageregate 
substance of the teeth enjoys incomparably more 
power of resisting both mechanical and chemical 
agency than the aggregate substance of common 
bone; the crown or exposed and working part of 
each tooth enjoys vastly more hardness and ex- 
terior strength than its root or unexposed and 
comparatively quiescent part; and the working 
surface of the crown, whether it consist of edge 
or points or lamine, enjoys exactly the amount 
of superior hardness or intrinsic diversity which 
fits it for performing its mechanical functions in 
the best possible manner with the least possible 
wear. 
The enamel is by far the densest and hardest 
of the three constituents of teeth; and will yield | 
fire with steel like flint, and is not easily acted 
on by even the best tempered files. It never oc- 
curs alone, but always as a coating to the other 
constituents ; and it serves so to temper the teeth, 
as steel tempers iron, that they may resist attri- 
tion, and continue unworn as long as the wants 
of the animal may require. In the incisors and 
cuspidates of the horse, it covers all the exposed 
portion; and in the grinders, instead of covering 
the surface generally, it forms distinct intertex- 
tured layers. It is supposed to consist of 78 per 
cent. of phosphate of lime, 6 of carbonate of lime, 
and 16 of gelatine; it has a crystalline compact- 
ness, but a minutely or very finely fibrous struc- 
ture; it is secreted from the membrane of the 
pulp; and it does not contain any cartilage, and 
is capable of complete solution in diluted nitric 
acid.—The ivory is very considerably softer than 
the enamel, yet harder than common bone; and 
it differs from the latter principally in contain- 
ing a greater proportion of phosphate of lime, 
and in some instances in containing fluorate of 
lime. It has a fibrous structure; and is secreted 
from the early pulp, and forms the rudimental 
and early portions of the teeth—The osseous 
cement is softer than the ivory, and contains a 
large proportion of animal matter, and somewhat 
nearly resembles common bone. It is regarded 
by some naturalists as an ossification of the se- 
creting membrane of the enamel; by others, as 
a specific secretion, like the enamel itself; and 
by others, as a correlative secretion with the 
enamel from one of two layers of a membrana- 
ceous capsule which surrounds the pulp of the 
ivory. 
Two sets of teeth are given to man and the 
greater number of quadrupeds,—the’ one tempo- 
rary, and commonly called shedding or milk teeth, 
—and the other permanent, and commonly called 
adult or full-grown teeth. The jaws grow much 
faster, and mature much earlier, in proportion, 
than the general system of the body ; and there- 
fore a temporary and comparatively small set of 
teeth is given them to suit their infant state, 
