APPENDIX A. 



THE EFFECTS OF DISTAL LEVERAGE ON THE rosTTION OP THE PRIMARY PETIOLE 



OF THE LEAVES OF JUTMOSA PUDICA 



When detached shoots of Mimosa pudica ore set in water and have a fresh nl**ptivo surface 

 provided by subaqueous amputation, of their lower ends, the pinnules under the KatMMt of light 

 presently assume their normal diurnal position, unless atmospherio humidit . bo abnormally low, or wb 

 they are exposed to the influence of direct sunshine. The primary petioles, however, ordinarily remain 

 somewhat depressed. If now all the pinnules be gently cut off, no sensible imrease in petiolar 

 depression usually occurs in spite of the escape of a certain amount of liquid from the tissues whi i 

 necessarily attends the procedure, and presently steady progressive elevation of the petiol. eta in. Tin- 

 amount of absorption of water taking place at the cut extremity of the ihoot is insufficient to secur- 

 elevation of the petioles so long as the inferior parenchyma of tfa primary pulvinus has i contend 

 with the normal leverage of the distal portions of the leaf, but suffices to do so wh< a the leverage i- 

 considerably reduced by the removal of the pinnules. 



Extreme elevation of the primary petioles occurs under the following conditions:- [. Trolongwi 

 depression of assimilatory function with continued respiratory loss and suppression of transpiration, su< h 

 as takes place during the course of the night: II. Exposure to an environment imp ving • voetti 

 transpiratory loss; III. Amputation of the pinnules or pinna>. The only common feature which 

 these conditions present is that they all imply the establishment of a considerable reduction in distal 

 leverage. 



Sudden, rapid movements of elevation of the primary petioles correspon • 1 i n g to the common Midden 



movements of depression, which so constantly manifest themselves, are of very rare occurrence. This 



is owing in part to the inherent structural features which distinguish the inferior and superior mnsp 



of parenchyma in the primary pulviuus, and partly to the fact that the superior mass is co-operated 



with by distal leverage, whilst the inferior one is directly opposed by it. Visibly progressive m< v.ments 



of elevation, and even sudden, rapid movements of a similar nature do, however, manifest themselves 



under certain circumstances. When a plant is enclosed within a saturated atmosphere and exposed to 



diffused sunlight, extreme expansion of the distal portions of the leaf and maximal elevation of the 



primary petioles occurs. If now it be suddenly exposed to relatively dry air, and con^ ently to 



sudden trauspiratory loss, elevation of the pinnules and deep depression of the primary petiole! occurs 



almost immediately in the majority of the leaves, and on returning it to the saturated atmosphere 



petiolar elevation sets in at once and progresses so rapidly as to be readily visible to the unaided eye. 



In such cases the movements of elevation, although rapid, are not of a sudden character; but movements 



of elevation, as sudden as any common movements of depression are, may be indued by exposing the 



puivinar tissues to circumstances inducing sudden losses in turgescence primarily localised to the superior 



parenchyma. If the rays of the sun be carefully focused upon the upper surfaces of primnry pulvini, 



the first movements which mauifest themselves are in many cases sudden movements of elevation of 



the primary petiole. The followiug table shows the results of fifteen experiments of this n tnre whi t 



were conducted on two successive mornings, and it will be seen that in nine instances sudden movements 



of elevation of the primary petiole occurred: 



Table I.— Remit a of focussing the rays of the sun on the upper surfaces of (he jrimanj pulvini of 



f Mimosa 



Depres 



2. Extreme elevation of the primary petiole, followed by depression 



Depre 



primary petiole, followed by 



Depression of the primary petiole 



Anv Roy. Bot. Gard.C alcutta Vol. VI. 



