combined agency of capillary attraction, and 
-_—— oo sik 
ASCENT OF SAP. 
954 
The fact of an internal flow of sap is thus ex- 
ceedingly obvious; and the fact that the sap dis- 
charged by bleeding is in the course of ascent, 
and not of descent, though not quite so obvious, 
is capable of easy proof. If several wounds are 
simultaneously made at different heights in one 
tree, the lowest will bleed before the others, and 
each succeeding one will bleed before that above 
it; ifa branch or stem of a vine be lopped asun- 
der, the standing part will bleed copiously, and 
the part cut off will not bleed; and if any large 
or wide incision in the trunk of a tree be exa- 
mined, the bleeding may, on minute inspection, 
be easily observed to proceed almost wholly from 
the lower side. But especially if any fibrous 
rooted or ligneous plant, with semitransparent 
| bark, be carefully lifted from the soil and imme- 
diately placed in radical contact with any inac- 
tive coloured infusion, such as pure water tinc- 
tured with madder root, the ascent of the 
| coloured liquid will speedily be observed from 
the roots to the very summit of the stem or ex- 
tremity of the larger branches, appearing in the 
interior of the plant like very slender longitudinal 
streaks or threads. Even the very velocity of 
the sap’s ascent has been made the subject of 
calculation. “To the stem of a vine cut off about 
two feet and a half from the ground, Hales fixed 
a mercurial gauge, which he luted with mastich. 
The gauge was in the form of a syphon, so con- 
trived that the mercury might be made to rise in 
proportion to the pressure of the ascending sap. 
The mercury rose accordingly, and reached as 
its maximum to a height of 38 inches. But this 
was equivalent to a column of water of the height 
of 43 feet 34 inches, demonstrating a force in the 
motion of the sap that, without the evidence of 
experiment, would have seemed altogether in- 
credible.’—{ Keith.| In a newly developed her- 
baceous stem, which as yet contains little fibrous 
or vascular tissue, the sap ascends chiefly through 
the pith; but in woody exogenous trunks, it rises 
through the alburnum or sap-wood; and in en- 
dogenous stems it is supposed to ascend through 
the bundles of fibrous and vascular tissue which 
constitute the wood. 
The cause of the sap’s ascent has been a proli- 
fic topic of disputation and theorizing among 
phytologists; yet, in spite of the mystery which 
hangs over even our most profound ideas of life, 
but with recognition of the peculiar and irresis- 
tible power which the principle of life exerts, it 
may be simply and very satisfactorily resolved 
into mere vegetable life,—or, as Keith more 
learnedly expresses it, “ the agency of the vital 
energies or affinities of the plant, merely with 
the subordinate aid of molecular infiltration.” 
But Grew ascribed the ascent of the sap to capil- 
lary attraction, and to volatility and magnetic 
tendency; Malpighi ascribed it to the contrac- 
tion and dilatation of air in the sap vessels by 
means of valves; De La Hire ascribed it to the 
ASH. 
valvular contraction and dilatation; Duhamel 
ascribed it to the combined agency of humidity. 
and heat; the elder Saussure ascribed it to a pe- 
culiar vital irritability similar to the peristaltic 
movement in the intestines of animals; Dutrochet 
ascribed it to the reciprocating agency of the 
positive and the negative electricities, or to an 
electric imbibition and exudation which he de- 
signated endosmose and exosmose; and De Can- 
dolle ascribes it to a vital contractility in the 
cells similar to the systole and diastole of the 
heart of animals. The whole question of the 
cause of the sap’s ascent, however, is too abstruse, | 
tvo much a matter of mere philosophy, to be 
worth a farmer’s serious attention, or to be cap- 
able of conversion to any very useful purpose. 
Even the channel of the sap’s ascent may, for all 
practical ends, be simply identified, in a general 
manner, with the softer tissues between the bark 
and the pith, and principally with the tubes of | 
the alburnum. 
ASCLEPIAS. The extensive genus of orna- 
mental herbaceous plants, popularly called Swat- | 
Low-Wort: see that article. The extensive na- 
tural order Asclepiadeze has the genus asclepias 
for its type, and comprises no fewer than twenty- 
four genera. This order is distinguished from 
every other by having its grains of pollen in a 
state of mutual waxy coherence within a sort of 
bag in the cells of the anthers. The plants of | 
the order are shrubs or herbs; they abound in 
an acrid and usually milky juice; and they are 
for the most part poisonous, and yet in several 
instances are wholesome and nourishing in their 
young shoots, Some are excessively fetid; some | 
are almost as powerfully emeticas the ipecacuanha 
of the drug-shops; and not a few have a curious 
appearance, and are more or less ornamental, | 
The most profuse vegetation of the order occurs 
within the tropics, | 
ASH,—botanically Fraxinus, A large and im- | 
portant genus of timber and ornamental trees, of | 
the olive-tree tribe. The English name is derived | 
from a Celtic word which signifies a pike, and | 
appears to have been suggested by the general | 
use of sticks and branches of ash for the long 
handles of implements; and the botanical name 
is derived from a Greek word which signifies 
separation, and appears to have been suggested 
by the facility with which ash timber splits. The 
trees of the genus, particularly those which grow 
indigenously in England, or which have been 
easily naturalized, are superior, for both utility 
and ornament, to all other tribes of hardy trees 
excepting the oaks, the pines, and the firs. Three 
species, the common, the warted, and the various- 
leaved, are natives of England; one, the Cauca- 
sian, is a native of the mountains of Caucasus, 
and was introduced to Great Britain in 1815; 
one, the narrow-leaved, though probably but a 
variety of the Caucasian, is a native of the south 
of Europe, and was introduced in 1821; two, the 
: 
| 
Aleppo and the small-leaved, are natives of the | 
