146 CUNNINGUAll 0^' FLUCTUATIONS TUEG ESCENClî.
applied to several ases, but in no instance wns the application followed by the oocurrQnce oi any
appreciable mo\'on]eDts, either centri f a gaily or centripetally.
Exi'eiument XIX.—July 25th, 8 a.m. Atmonpltcric feiiiperalure Htumdity per cent. The
vionwig icns cloudy; tenj heavy rain had fallm shortly before and eccrything wai tenj >cH.—Seariog oi axes
was followed only by very slow, imperfect action oonEueJ to the first leaf beyond the point of
application.
Now were the effects which, under average conditions of humidity, follow the application of heat to
axes dependent on the propagation of stimulant fluctuations in pressure coaduoted along any closed
system of tubes containing liquid such as Ilaberlandt'a " Reizloitende system," it is clear that, in place
of diminishing and ultimately disappearing with increased humidity, they ought to increase as it
increases. Tliey ought to increase with any conditions favouring increased turgidity througliout the
system, wliereos in fact Ihey follow a precisely opposite course. But such decrease and abolition of
3 precisely what ought to occur if the phenomenon of spreadiug centrifugal movement which
inder ordinary
current
humidity there
ndii
imstanees be the outcome i
; from the roots. Under
díítioii oE surplus water witli
sufEoes to maintain fuU tii:
if an obstructive gaseous interference with the
ordinary conditions of atmospheric and telluric
ill the water-conducting i-ystem, and the stream
gescence of the tissues in spite of continuous
' obstruction to the continuity of the
betweun supply and loss of water in all distally situated
5 is dypeiiJeiit on maximal turgescence in the tissues o£
0 must inevitably tend to cause a departure from it.
c humidity are maximal, root-supply becomes escossivs'
aum, and with this a surplus stock of water must
J system. The latter no longer represents a simple
i t the distal extremity in the
ing a large store of water from
bulk of water contained within
continuously withdrawn from it to
Tl,e
; the latter only
transpiratory loss. Under such circumstiinces
once tind to disturb tlie pre-esistent equilibri
p a r t s ; and as the diurnal positlou of the h
the motor organs, any disturbance of tliis n:
But where conditions of atmospheric and telluric hi:
at)d transpiratory loss is reduced to 'a,minimum,
tend to acoumuiato within the water-con ducting s_v
Fystero of channels traversed by a stream of wat'
Bnme bulk as it enters at the proximal one, but
which only a very small quantity is constantly being withdrawn,
the water-conducting system is greatly in exccss of tliat whioli
maintain full turgescence under tlio conditions of minimal transpiratory loss, and consequently the
occurrence of a temporary obstruction of root-supply is of no omisequence in respect to the maintenance
of turgescence. The diurnal position of the leaves is determined by the fact that certain masses
of tissue iu the motor organs are endowed with e.xcessive assimilatory and osmotic properties under the
influence of solar stimulation. But the application of lieat to a point in an axis does not afl'ect the
ossirailatory and osmotic properties of tlie motor organs of tiie leaves in any way, and consequently,
BO long OS t h e water-conducting system contains a supply of water from" which th«y can satisfy their
osmotic capacities, there is no reason wliy any fluctuations in their turgescence should attend the application.
Now a store of surplus water has aooumulated within the water-conducting system under the
influence of the previous and existent conditions of humidity, so that a temporary obstruction to the
access of any additional supply is of no importance wluitever in resard to the maintenance of turgescence,
and consequently no movements attend its establishment. The absence of movements in this
case is precisely parallel to tlie absence of movements attending the separation of leaves or shoots
from a plant under conditions of excessive humidity. In both cases alike there ia an arrest of rootsupply
of water; but, iu the ease of detneb-nent, not only is tlie arrest an absolute and permanent one,
but it is accompanied by a certain amount of active loss of liquid from the out en-l of the petiole or
shoot ; wliereaa on the application of htat to the tissues of a mature axis mere temporary obstruction
to loot-supply is present. In both cases alike the maintenance of tlie turgescence of the motor organs
is for the time being fully provided for by the local store of water within the water-conductiug system ;
and consequently any brief, temporary arrest of root-supply is incapable of iailuoing the occurrence of
any movements, and any permanent one can give rise to moremeats only after the gradual expenditure
oí the surplus water stoied up withiu the water-conducting system. In neither case does any immediate
effect follow the anest of root-sujiply ; and where the arrest is only temporary and renewed
sujiply sets in ere expenditure of the store-nattr has occurred, no movements at all will occur. Where,
or the other hand, the arrest i
will ultimately set in in coe
the surplus water.
APPENDÎCKS.
I permanent one, movements oF a slow,
quenco of the gradual fall in turgoscon
nsensibly pi-ogressiv© clmrocter
3 attending the expenditure of
APPENDIX G.
EXPERIMEKTS DEMONSTRATING THE PEOPAG.\TION OF TItE CO>?niTIONS GIVIXG RISE TO
MOVEMENTS THItOUOn AREAS OF DEAD TtSSaK DEVOID OF ANY LIVING PEOTOPL.iSM OR
SYSTEM OF TUUGID SIEVE-TUBES.
ExrERiMENT I.—An axis of Mimosa jtwlka was thoroughly seared at two distinct levels by
means of
measured
both the
3 fnim the
the low..r
il position,
the applicotion of the points of a strongly heated pair of forceps. The higher seared area
O-BO" and the lower O'S" in length, and subsequent microscopic exaraini
tissues had been entirely killed throughout the entire thickness of th
portion of the
and above the
an open flame ^
lower seared arc
of the leaves beneath the
I the
beyond thi
Expe:
with heated forceps. On th
leaves, both below and abo\
tips of the terminal pinnules of
;howod that
i. One leaf a:
between the two seared areas, and several others were situated belojpper
one. After the leaves had completely recovered the normal diu
.s applied to the tips of tho tei-minal pinnules of
of the axis, and universal propagation of movements took place; all the leaves
e beneath the lower seared area, the one between the two seared areas, and those
one alike showing rapid petiolar depression and pinnulnr elevation.
n - A n area O S" in length in the axis of a small pot-plant was thoroughly seared
following day the seared area was perfectly dead, dry. and brown ; but the
it, were in full, normal, diurnal position. When flamo was applied to tho
distal pinna on one of the leaves beneath the seared area, complete
1 occurred in it, and propagation of presently followed throughout the entir
thi
la course. On the following
)f flame to tho tips of the
seared area was iollowed by
ExrrviiiiitEST III.—An axis was thoroughly seared nt two points in
day all the leaves were in normal, diurnal position. The application
terminal pinnules of a distal pinna ,of one of the lenvcs beneath tl.e lowe:
movements extending over all the leaves on the axis, incind;--
areas. The length of each of the seared areas v
that the tissues had been thoroughly killed throughout tin
ae arising between the two seared
ibout 0-4f>", and mii;roscopical examination showed
ire thickness of the axis.
ExPEnn-EST I V . - A pot-plant, consisting of a single axis bearing si., leaves, was thoroughly seared
and killed at two points, one situated between the second and third leaves from the base of the axis and
the other between the third and fourth leaves. After all the leaves had completely recovered the
.lorniDl diurnal position, the tips of a pair of heated forceps were applied to the base of ti.e axis and
rapid centiifugal propagation of movements presently occurred in all six leaves,
Expeiii>.knt V . - A plant was treated iu the same way as that of the preced
complete recovery of the normal diurnal position the application of the point >
point near the bnse of the axis was followed by complete propagation of mover
along its course, bcneiith, between, and above the seared areas.
ig exporiiuent. After
• heated forceps to a
mts to all the leaves
Such experiments conclusively prove that the propagation of movements along the c
9 of axes is
neither dependent on any continuous tracts of living protoplasm, nor on the existence of any oontmuons
system of turgid tnbes along the course of which eudden fluctuations in pressure may be transmitted.
The thorough searing of the tissues of tho axis implies not merely local death, but local absence
of turgidity in the tissues. The seared areas, in place of any longer being sites of active turgescence,
are sites which afi:ord abnormal facilities for tho escape of liquid from the tissues, as is clearly indicated
by the fact that, unless under conditions of excessive atnospherie humidity, the leaves which ara situated
distally soon begin to indicate the presenoe of insufficient water-supply by their incapacity to assume
tho maximal diurnal position. Tho thorough seariug of the tissues of the axis just as effectually
iutorrupts ihe contmuity of tho tiivgid system of sieve-tubes as any local excision of the bast docs, and