1911.] 



The Origin of Osmotic Effects. 



227 



more recent communication,* in which we have discussed observations made 

 later in the year with leaves of Aucuba japonica and a number of other 

 plants, we again called attention to the osmotic effects conditioned by 

 hormones and the suggestion was advanced that the translocation of nutritive 

 materials takes place periodically. 



Taken in conjunction with those made by Adrian Brown, our observations 

 show that the outer differential septa in plants are permeable only by 

 substances of a particular type — apparently only by substances having but 

 slight affinity for water ; consequently, if the argument apply to plant cells- 

 generally, ordinary nutritive materials, such as the sugars, for example, 

 cannot pass through unless the septa are in some measure broken down. 

 It almost stands to reason that the translocation of carbohydrates and many 

 other materials must take place periodically: that at some times the cell 

 walls must be permeable whilst at others impermeable. As we have already 

 pointed out, Darwin's work on insectivorous plants appears to be full of 

 evidence that such is the case. 



It is abundantly clear from the behaviour of Saxifraga sarmcntosa, for 

 example, that the cells generally are lined with a septum which is differentially 

 permeable. When placed in a solution of greater osmotic tension than that 

 within the cells, the coloured fluid is retracted in the well-known way ; this, 

 effect is easily reversed and the change may be brought about time after time- 

 provided that the membrane enclosing the cell contents remain uninjured. 

 The effect cannot be produced after exposure to chloroform and there are 

 many other substances which act similarly ; it is therefore to be supposed 

 that it is conditioned by the differential permeability of the thin protoplasmie 

 membrane which lines the cell. 



In the account of our experiments with leaves of Primus laurocerasus we- 

 stated that, of the three substances into which the glucoside characteristic 

 of the plant, prulaurasin, is resolved — glucose, benzaldehyde and hydrogen 

 cyanide — the last two act as hormones, each being capable of conditioning 

 hydrolysis. In studying the action of these and other hormones, as was to< 

 be expected would be the case, significant differences have been brought 

 to light ; we propose to make these differences the subject of careful study. 

 On the present occasion we desire to call attention to the special effect 

 produced by hydrogen cyanide, as this appears to us to raise issues of 

 peculiar and wide significance. 



If kept in water, leaves such as those of Prunus laurocerasus or of Aucuba 

 japonica not only remain unchanged during many days but nothing diffuses 

 * "The Function of Hormones in .Regulating Metabolism," " Annals of Botany,' 1911,. 

 vol. 25, pp. 507—519. 



