



APPENDICES. 



109 



position, and such diminution may be effected as the result either of absolute diminution in loss or of 

 absolute increase in supply. Hence normally rooted plant i which have pass d into the nocturnal 

 condition diurnally may be caused to resume the normal diurnal one by exposing them to ooiidit m 

 implying either diminished transpiration or increased root-supply : in other words, bv exposing them to 

 a more humid atmosphere, or by adding water to the soil iu which they are rooted. 



APPENDIX C. 



THE INFLUENCE OF VARIATIONS IN DKGBER OF ASSIMILATOBT ACTIVITY o\ THE OCCTKKFN< I 



AND CHAEACTEK OF THE MOVEMENTS OF THE LEAVES OF MIMOSA PI MCA. 



Variations in osmotic capacity in the tissues of the motor organs connected with variation is tl 



activity of assimilatory function come into play as intrinsic factors affecting the liability of the leaves 

 to undergo sudden movements. The degree of "irritability" of plants exposed to < I litions iranl njr 

 excessive atmospheric and telluric humidity is conspicuously much greater aft.-r sundown than whilst 

 they are exposed to full solar stimulation; and, whilst the sudden exposure of a plant to the arid 

 atmosphere of a simple sulphuric-acid chamber is only attended by slow and gradually progressiva 

 movements of the leave?, exposure in a chamber containing both sulphuric ne;d and chloi form 

 is followed by the occurrence of rapid pinnular movements. Osmotic capacity iu the cell-sap 

 determines the existence of turgescence, aud iu maintaining it has constantly to contend with 

 the filtrative escape of liquid incident on the elastic recoil of the extended cell-walls. Any fall 

 in osmotic property in the cell-sap must favour the occurrence and rapidity of processes of 

 filtration, and consequently the occurrence of rapid fluctuations to the degree of turgescence of 

 the tissue; hence factors, which are quite incapable of giving rise to rapid and considerable 

 fluctuations in turgescence whilst osmotic capacity is high, may well become cflicient (o do so when 

 it has undergone considerable decrease. The effect produced by any factor favouring the et ape of 

 liquid from the interior of the cell-cavities, and consequently making for diminution in turg. > ence 

 of tissue, must necessarily be modified by the degree of osmotic capacity in the cell-sap which 

 is a factor making for local retention of liquid. Consequently depression of assimilatory activity, as it 

 normally implies a decrease in osmotic capacity, not only comes into play to give rise to slow, progressive 

 movements when it acts alone, but has also an important influence in modifying the extent to which 

 the sudden incidence of other factors making for decreased turgescence will be capable of giving rise 

 to the occurrence of sudden movements. The ordinary periodic movements of the leaves aie manifestly 

 determined by fluctuations in turgescence in the tissues of the motor organs connected with fluctua- 

 tions in the degree of assimilatory activity incident on the presence or absence of solar stimulation, 

 and it is evident that any other factors of fluctuations in turgescence must be liable to have their 

 effects modified according as they act in unison with, or in opposition to, the assimilatory influences 

 affecting turgescence. The removal of solar stimulation determines the occurrence of a fall in turges- 

 cence which makes for the assumption of the nocturnal position, and if another factor making for the 

 same thing comes into play simultaneously with it, it is evident that the effect which the latter will 

 produce is likely to be greater than when it comes into play at a time when the conditions of assi- 

 milatory activity, in place of favouring the assumption of the nocturnal position, favour the maintenance 

 of the diurnal one. Hence, other things being alike, •♦irritability" tends to attain its maximum 

 at sundown owing to the fact that, at this time, any factor making for decreased turgescence acts in 

 co-operation with a coincident fall in assimilatory activity which makes for the same thing. The absence 

 of solar stimulation, however, not merely favours the occurrence of rapid movements under the influ- 

 ence of other factors making for losses in turgescence in the motor organs, but also affects the 

 peimanence of the position which has been assumed under the influence of the latter. That this is the 

 case is clearly demonstrated by the results of experiments such as the following one : 



Experiment I.— A shoot of Mimosa pudica, hearing five leaves, was detached from a plant at 

 6-40 a.m. without any special precaution to avoid disturbance of the leaves, all of which, as is usual under 



