u THE CAUSliS OP FLUOTUAriO>!S II^ TUKGliSCENCli
of SOc'.c. Ill this case about oOo.c. hatl traversed the boiled portion of the petiole
within twenty-foiu- hours, for the loss b y mere evaporation in a chock bottle of water
was almost inappreciable during the same period. The nine pairs of piunie which
had been left on tho leaf remained quite green and tm-gid.
Experiment FZZ7.—Two leaves of Cassia alala were taken, and all the pinnaj save
t h e two terminal pairs were cut off. One specimen was then entirely immersed in
boiling water for a minute, and the lower part of the petiole of the other was similarly
treated. The ostremities of the petioles were then freshly divided under water and
set side b y side in marked water-bottles. On the following day the water in the bottle
containing the wholly boiled specimen showed a loss of lOe.c., and that in the other
one of Uc.c. The pinna; in the wholly boiled leaf were quite flaccid, drooping, and
brownish, whilst those in the other were fully expanded, green, and turgid. Twentyfour
hours later an additional loss o£ 7c.c. was registered in the former and one
of 8c.c. in tlie latter specimen. The araomit of water absorbed by the wholly dead
leaf during tlie entire course of the experiment was only oc.c. less than that in the
case ia which the lower part of the petiole alone had been boiled; but in estimating
the amount of absorption duo to the vital activities of the tissues in tho latter it must
be borne in mind that the amount of loss due to siinplo evaporation in it was certainly
much less than in tlie other specimen, in which the retentive power for fluid connected
with functional activity had been totally abolished.
Experlmenf IX.—Two loaves of Cassia data, each bearing eight pairs of pinnre
after tho removal of tho basal pair, were set sido by side in marked water-bottles, the
lower part of the petiole having in one case been boiled for two minutes and in tho
other left intact. Twenty-four hours later tlie pinntc of both leaves alilce were fully
expanded, green and turgid, and the loss of water registered by each bottle was 23c.c.
The boiled portion of the petiole of the one leaf was quite brown and the cortical
parencliyma flaccid. One phenomenon whicli presented itself in this case was that
the absorption of water was primarily more rapid in the specimen in which tin? lower
part of the petiole had been boiled than in that in whidi it had been left intact, this
no doubt being due to the aspiratory action of the gaseous contents of tho waterconducting
system on contracting under the influence tho fall of temperature subsequent
to removal from tho boiling water.
I t appears clear from the previoas expsriments that the action of heat and
chloroform on living vegetable tissues is strictly localised to tho parts directly exposed
to iheir influence, and that, even where the exposure rcsulrs in death, there is no
propagation of any effects to protected parts, however close to and continuous with
the injured ones they may be. In other words, there is no evidence that tJie death
of the protoplasts in one part produces any appreciable direct results on the wellbeing
of neighbouring but protected parts. The quantity and quality of the watersupply
conducted by the vascular tissues remains inappreciably affected by chloroform ;
and although heat may temporarily affect tho former, due to the expansion of tlie
gaseous contents of tlie conducting system which it induces, the obstraction thus arising
is transitory, and this being so, in neither case does tho mere loss of turgoscence
and death of neighbouring parts ordinarily give rise to any appreciable effect?. Very
different results ensue, as is shown by the next experiment, whore the reagent which
IN THE MOTOR ORGANS OF LEAVES.
is primarily locally applied is readily sohible in water, and therefore liable
conducted by the stream of fluid traversing the vascular tissues.
Experiment X—Two leaves of Cassia stmatrana were taken and set with the
bases of their petioles immer.sed in water and subaqueously divided in order to permit
of freo absorption. One of them (a) was now along with its water-vessel introduced
into a beaker containing a little ammonia, the mouth of the beaker being closed by a
cork securely luted down and around tlie rachis, so that whilst the lower portion
of tho latter and the basal pinn® were enclosed in the beaker and exposed to tho
ammonia vapour, the upper portion and the distal piimaj projected free into the air
aod had no immediate relation to the reagent. Tlie other loaf (¿} was similarly
treated, only in tliis case the beaker contained chloroform in place of ammonia. The
pinuo3 o£ («) which were within tiie beaker rapidly acquired a dark colour, M-hilst
drops of black fluid began to exude from the surface of the rachis, and shortly
afterwards similar changes began to manifest themselves in the part of the loaf outside
tho b.-aker, the piun® drooping and darkening in colour especially along the neighbourhood
of their midribs, and exudation beginning to appear on the rachis. Twenty-four
hours later the leaf was %vilted throughout, the pinnce gxeatly blackened and the
rachis thickly studded with drops of black fluid. The portions of (b) which were
included in the beaker were also very rapidly affected, the pmnie - becoming flaccid
and of a brownish olive colour and the rachis exuding drops of pale yellowisli fluid,
but tliere was no extension of these changes to the portion of the leaf beyond the
cork, the pinua3 retaining their original colour and turgidity and the racliis showing
no signs of exudation. On the follo-wing day the free jiortions oi tho leaf remaitied
ontii-ely unafleoted, and the pimu-o were M l y expanded, Inrgid and of their original
bright green colour, -whUe the petiole, oven down to the snrfaco of tho ooii, showed
no signs of any change.
Here, m both leaves alike, the tissues which were directly exposed to the iniluence
of the reagent -wore rapidly killed and rendered flaccid by loss of turgidity, but
whilst in one ease these changes extended rapidly and completely throughout the
entire leaf, in the other there was no propagation of them to tho protected parts.
Both reagents rapidly induce death in tissues dir-cctly exposed to their influence; but
whilst chloroform is only very slightly soluble in water, ammouia is excessively so,
and therefore is readily conveyed to distal areas. Such exporimeirfs afford no evidence
of the transfer of any influences by means of the protoplasmic continuity of the
tissues, the complete death of great masses of tissue failing to give rise to any
appreciable efiecls in immediately eontigaous parts so long as the water-supply of
the latter remains unafiectod, but they imcquivooally show how rapidly changes may
bo propagated to distal areas by means of alterations in their water-supply. This
is a question which will bo recurred to subsequently, aud it is merely alluded to
hero becaase the phenomena of the experiment appear- so clearly to suggest that it
is to the water-conducting system and not to any system of continuous protoplasts
that we nnist look for an explanation of the propagation of effects from one area
to another in the organism of any of the higher plants.
The above experiments have demonstrated very clcarly that exposure of T e s t a b le
tissues to excessive heat gives rise to effects similar to those which follow theii' exposure