Permeability 209 
these conditions because the pressure balancing the hydrostatic pres¬ 
sure of the cell, the turgor pressure, which must be uniform through¬ 
out, is made up of the sum of the wall pressure and a component of 
the pressure exerted by neighbouring cells, which may vary at 
different points on the wall of the cell under consideration, since a 
number of cells are concerned, namely, all the neighbouring cells. 
Hofler supposes that under these conditions water saturation is 
reached sooner than it would be in the isolated cell because in addition 
to the inwardly directed pressure of the stretched wall of the cell 
itself there is the pressure exerted by the neighbouring cells to 
prevent further increase of the volume of the cell. If this view 
is correct, Hofler points out a very significant consequence of it 
in reference to the suction pressure. As with progressive intake 
of water the turgor pressure must increase to its maximum more 
rapidly than it would if isolated, it follows that the suction pressure 
must increase more rapidly with decreasing turgidity in the case of 
the cell in a tissue than in the isolated cell, other things being equal, 
since the suction pressure is equal to the osmotic pressure less the 
turgor pressure. That is, the suction pressure can vary greatly within 
a small range of turgidity. This may be of great importance from an 
ecological point of view. 
