IN THE MOTOR OBGANS OP L BATES. 



35 



The results of this experiment very clearly show that the action of osmic acid in 

 preventing a loss of turgescence on the death of the tiiiuei is quite distinct from that 

 of ammonia. The loss of turgescence is greatly retarded, and may even initially be 

 obscured altogether, owing to the addition of new weighty constituents of the tiiiues, 

 but there is no absolute arrest of it after a certain point as there is in the case of 

 ammoniated tissues when freely supplied with water. In the case of the ammoniated 

 tissues the evidence points unequivocally to an artificial maintenance of osmotic property, 

 in that of those acted on by the osmic acid to the establishment of an obstruct ion 

 to filtration impeding the action of the elastic recoil of the cell- walls in effecting tho 

 discharge of fluid from the interior of the cell cavities. Tho total loss of weight in 

 the case of the ammoniated leaf during a period of twenty- three days amounted oc 

 to 1*47 grammes, or 5*4 per cent., aud of this M9 or 4*3 per cent, occurred within 

 the first twenty-four hours; the loss in the leaf exposed to osmic vapour during a 

 period of nine days amounted to 4*6 1 grammes or 16-6 per cent., and was steadily 

 progressive and unaffected by the freest supply of water to the tissues, whereas in the 

 ammoniated leaf immediate recovery of weight followed renewed supply of water. 



If the filtrative resistance of the protoplasts of a tissue be artificially elevated, as 

 it appears to be under the influence of osmic acid, tho loss in turgescence normally 

 accompanying loss in osmotic capacity in the cell-sap will be retarded 1m auso tho 

 elastic recoil of the cell- walls now encounters an abnormal opposition; and if a mass of 

 turgid tissue be exposed to sufficient external pressure, a diminution in its turgescence 

 will necessarily take place apart from any loss of osmotic capacity, because filtration 



will now no longer be dependent merely on the elastic recoil of the cell-walls, but on 

 this, aided by external pressure. But whilst this is the case — whilst the actual degree 

 of turgescence present in any given tissue is liable to be affected by its filtrative as 

 well as its osmotic condition — there is no evidence to show that, under normal circum- 

 stances, any mere alterations in the inherent filtrative properties of the protoplasm of a 

 tissue, apart from alterations in the osmotic properties of its cell-sap, are efficient to give 

 rise to appreciable changes in its turgidity ; and the belief that they do act in such 

 a fashion is simply based on the arbitrary assumption that the exercise of contractile 

 function — that mere change of form in the living elements of a tissue— is capable of 

 giving rise to alterations in its turgescence, which, of course, necessitates the second 

 assumption that the change in form is accompanied by a change in filtrative resistance. 

 The protoplasm in ammoniated leaves of Kalanclm has probably lost considerably in 

 filtrative resistance, and yet the tissues retain a high degree of turgescence; whilst, in 

 cases where the leaves are exposed to tho influence of the vapour of chloroform, there 

 is no reason to suppose that there is any depression of filtrative resistance, and yet 



total loss of turgescence occurs. 



The belief that the essential determinant of turgescence lies in certain physical pecu- 

 liarities of protoplasm, and not in the properties of its products, and that any losses in 

 turgescence which are related to functional causes are due to increased filtrative power 

 in the protoplasts of a tissue, has no doubt arisen because of the striking fluctuations 

 in turgescence accompanying depression or cessation of protoplasmic activity in cases 

 where the osmotic products of the latter, on the presence of which turgescence depends, 

 are very unstable, and must therefore be constantly renewed in order to the maintenance 

 of turgidity. In the vast majority of cases, the protoplasmic products on which the colour 

 and turgescence of the tissues depend are very unstable, and hence any considerable 





Ann. Roy. Bot. Gard. Calcvtta Vol. VI. 



