DEC 
DECIDUUS, in botany, a term expres- 
sive of the second stage of duration in 
plants, but, like caducus, susceptible of dif- 
ferent senses, according to the particular 
part of the plant to which it is applied. A 
leaf is said to be deciduus which drops in 
autumn ; petals are deciduus which fall off 
with the stamina and pistillum ; and this 
epithet is applied to such flower-cups as 
fell after tlie expansion, and before the 
dropping of the flower. This last is exem- 
plified in berberry, and the flowers of the 
class Tetradj-namia. 
Most plants in cold and temperate cli- 
mates shed their leaves evei-y year. This 
happens in autumn, and is generally an- 
nounced by the flowering of the common 
meadow saffron. The term is only applied 
to trees and shrubs ; for herbs perish down 
to the root every year, losing stem, leaves, 
and all. All plants do not drop their leaves 
at the same time. Among large trees, the 
ash and walnut, although latest in unfold- 
ing, are soonest divested of them : the lat- 
ter seldom carries its leaves above five 
months. On the oak and horn-beam the 
leaves die and wither as soon as the colds 
commence; but remain attached to the 
branches till they are pushed off by the 
new ones, which unfold themselves the fol- 
lowing spring. These trees are doubtless 
a kind of evergreens ; the leaves are proba- 
bly destroyed only by cold ; and, perhaps, 
would continue longer upon the plant, but 
for the force of the spring-sap, joined to the 
moisture. 
With respect to deciduus trees, the fall- 
ing off of the leaves seems principally to 
depend on the temperature of the atmo- 
sphere, which likevvise serves to hasten or 
retard the appearance in question. An ar- 
dent sun contributes to hasten the dropping 
of the leaves. Hence, in hot and dry sum- 
mers, the leaves of the lime-tree and liorse- 
chesnut turn yellow about the 1 st of Sep- 
tember ; whilst, in other years, the yellow- 
ness does not appear till tlte beginning of 
October. Nothing, however, sontributes 
more to hasten the fall of the leaves than 
immoderate cold or moist weatlier in au- 
tumn ; moderate droughts, on the other 
hand, serve to retard it. It deserves to be 
remarked, that an ever-green tree grafted 
upon a deciduus, determines the latter to 
retain its leaves. This observation is con- 
firmed by repeated experiments, particu- 
larly by grafting the laurel, or chei-i^-bay, 
an ever-green, on the common cherry ; and 
the ilex, or ever-green oak, on the oak. 
DEC 
DECIMAL arithmetic, the art of com- 
puting by decunal fractions. 
Decimac fraction, that whose denomi- 
nator is always 1 , with one or more cyphers : 
thus, an unit may be imagined to be equally 
divided into 10 parts, and each of these into 
10 more ; so that by a continual decimal 
subdivision the unit may be supposed to be 
divided into 10 , 100 , 1000 , &c. equal parts, 
called tenth, hundredth, thousandth parts of 
an unit. In decimal fractions, the figures 
of the numerator are only expressed, the 
denominator being omitted, because it is 
known to be always an unit with so many 
cyphers as there are places in the numerator . 
A decimal fraction is distinguished from an 
integer with a point prefixed, as .2 for ■^, .34 
for .567 for &c. The same is 
observed in mixed numbers, as 678.9 for 
678^, 67.89 for 67-f^, 6.789 for 6 ®, &c. 
Cyphers at the right hand of a decimal 
fraction alter not its value ; for .5 or .50 
or .5000 is each of them of the same value, 
equal to or i : but cyphers at the left 
hand, in a decimal fraction, decrease the 
value in a tenfold proportion ; for .05 is 
.005 is ^' 55 , .0005 is ^olooj 
As the denominator of a decimal is al- 
w'ays one of the numbers 10 , 100 , 1000 , &c. 
the mconvenience of writing thesa denomi- 
nators down may be saved, by placing a 
proper distinction before the figures of the 
numerator only, to distingiiish them from 
integers, for the value of each place of 
figures will be known in decimals, as well as 
in integers, by ttieir distance from the 1 st 
or unit’s place of integers, having similar 
names at equal distances, as appears by the 
following scale of places, both in decimals 
and integers. 
&c. 6666666 666666 &c. 
S- c 
S2 S 
S- ta- 
re n- 
B o 
10 e 
A » 
2 s ^ 
s 
Q, 
g 
9» 
S 
i=u 
a.- 
a* 
Sn 
e/i V) ^ ui 03 
c -B X! "W C 
0 ) 9 > B g a o 
eS «« es 
s S3 5 P'S 
0 0 0 0 9 
eS3 pO ^3 
^ -w 
§ -a 
-a B 
Decimal fractions are easily reduced into 
a common denominator, by making, or 
even supposing, all of them to consist of 
the same number of places ; so .3, .45, 
.067, .0089, may be written thus, .3000 
.4500, .0670, ,0089 ; all which consisting 
of four places, their common denomina- 
tor is an unit with four cyphers^ namely 
10000. 
