



38 



THE CAUSES OP FLUCTUATIONS IN TURGESCENCE 



demonstrate that, in 



both alike, the essential determinant 



the relation bet 



supply and loss of water 



Experiment Z— At 2-30 p.m. of a bright afternoon in November, the leaflets of four 

 plants of Cassia alata, growing in rather small pots, were all in almost complete nocturnal 

 position, whilst those of a plant of the same species, situated side by side with them 

 and under precisely the same conditions in regard to insolation, but growing in the ground, 

 were in a state of full expansion. One of the pots was flooded with water, and an hour 



ose of the other 



the leaves of the plant in it 



almost fully expanded, whilst 



pot-plants remained as before in the nocturnal position. At the same time the leaves of 



an Eranihemum grow 



beside the Cassias were very considerably wilted 



H 



there 



were indices to the occurrence of general loss of turg' 



the Eranthemum leaves 



and of local loss of turgescence in certain masses of tissue in the leaves of the Cassias 

 in pots, determined, in the latter at all events, simply by defective root-supply in relation 



to transpiratory loss. 



I 



Experiment II.— At 1-30 p.m. on another day the leaves of two pot-plants of Cassia 

 alata had their pinnae in almost fully developed nocturnal position. One pot was flooded 

 with water, and at 2-50 p.m. the pinnae of the plant in it were almost fully expanded, 

 whilst those of the other remained as before. 



Experiment III.— Two pot-plants of Cassia alata were set side by side on a flat 

 masonry roof, so as to be fully exposed to the sun all day. At 1-20 p.m. of December 

 10th, one of them had its leaflets in the nocturnal position and the other its leaflets 

 nearly in the same state. The pot containing the former was flooded with water, and 

 three hours later the plant in it was fully expanded, whilst the other remained as before. 

 The following day was a cool, dry one, with only feeble sunshine, owing to the general 

 clouding of the sky ; but in spite of this both plants were in partial nocturnal position at 

 1-30 p.m., the development of the nocturnal position being much more advanced in the 



plant 



the pot which had not been flooded 



the other. The former plant was now flooded 

 only a 1 



the previous day than in the plant in 



Twenty-four hours later its leaflets showed 



very slight tendency towards the assumption of the nocturnal position, wh 

 those of the other plant had to a great extent assumed 



latter plant was flooded, and at 4-30 the leaflets were found fully expanded, whilst "those 

 of the other plant remained as before in the initial stages of the nocturnal position 



it. The pot containing the 



It would be easy to multiply th 



but, as the results were of a uniform nature 



record of experiments of this nature indefinitely 



yctitropic leav 



clearly show the influence which 



would be superfluous to do 



Other 

 exerted on turgescence by 



variations in the relations between root-supply and transpiratory loss. In warm, relatively 

 dry weather, and under like exposure to sunshine, the leaves of pot-plants of Pithecolobium 

 saman will be found to be in the fully developed nocturnal position, whilst those of plants 

 rooted in the ground are in the fullest expansion. 



sum a trana 



T 



plants growing side by side and 



rooted in the ground and the other in the 



So again with the leaves of Cassia 

 qually exposed to the sunshine, but 



wall, day after day 



afternoon during warm dry weather will respectively have their leaflets in full expansion 



and in the nocturnal position. In the above instances the most influential factor 

 giving 



rise to diminished turgescence under otherwise favourable circumstances 



in 



was 



