THE CELL-MEMBRANE. 361 



insoluble pectates, containing no cellulose, and lined on 

 each side by mixed layers of cellulose and pectose. From 

 that point onwards it undergoes throughout its substance 

 continuous transformations which modify the disposition of 

 its constituent substances, the middle lamella becominof 

 conspicuously increased in amount. 



In this connection it is well to remember Wiesner's 

 hypothesis of the dermatosomes in the wall, as it is evident 

 that such transformations of material may well be brought 

 about under the influence of such protoplasmic bodies in 

 the interior of the membrane. 



The mode of deposit of the projections or concretions 

 of calcic pectate may perhaps aid us in forming a true con- 

 ception of what takes place. I hese pectates gradually tend 

 towards the outside of the membrane, passing possibly as 

 soluble pectic acid in its substance, and being combined 

 with the metallic base at the external surface or in the 

 intercellular space. In the young growing cell, just behind 

 the zone of cell division at the growing point there is the 

 maximum of turgidity or osmotic pressure. It is quite con- 

 ceivable that in a free cell this is sufficient to cause a stream 

 of soluble bodies to pass across the substance of the cell 

 membrane from within outwards. This indeed would lead 

 to the extrusion of such soluble pectates, or pectic acid, 

 which may be well formed from the pectose in the mem- 

 brane by the action of the dilute acid of the cell-sap, into 

 the space around the cell, or in a tissue, into any inter- 

 cellular passage. But in the case where the cells are not 

 free, but have their neighbours pressing upon them, as they 

 have in the young part of the growing zone, any membrane 

 will be subject to a pressure from each side, owing to the 

 turgidity of the contiguous cells. In this case the stream 

 of pectates would not pass out of the cell, but would tend to 

 accumulate in the middle line between the two pressures, 

 in the region that is where the middle lamella speedily 

 becomes recognisable. 



In connection with the formation of the calcic salt from 

 the acid body, we may recall Fremy's observations on the 

 ferment which he discovered in the root of the carrot. 



