184 BOTANICAL GAZETTE [SEPTEMBER 
of the lima bean to demonstrate osmosis in his elementary classes in 
plant physiology. The coats are merely tied over the ends of glass 
tubes. His experience has been that the coats are irregular in their 
behavior, and that successful use demands the testing of the 
membranes, and the choice of those whose behavior with a definite 
strength of solution is uniform. Thus chosen, the membranes may 
be used to demonstrate admirably PFEFFER’s discovery that osmotic 
pressure varies directly with the concentration of the solution. 
Recently Lavison (24) studied the entrance of salts into the 
roots of plants and showed that the cellulose “frames” (cadres) 
around the cells of the endodermis are impermeable to certain salts, 
and that entering salts must therefore pass through protoplasm in 
penetrating the root beyond the endodermis. Later (25) he made 
the further observation that the cellulose cell walls forming the 
periclinal walls of the endodermis behave toward entering salts like 
the protoplasm itself. That is, those salts which are excluded by 
the protoplasm are excluded by the walls also. Lavrson does not 
say that the walls are selectively semipermeable, but that is seem- 
ingly the only possible interpretation of his observation. It should 
be noted that this applies only to the young cellulose walls. 
All of this evidence points to semipermeability as a widespread 
phenomenon among lifeless plant membranes. Of course, the 
membrane must be permeable to water if it is to be osmotically 
active. The thin skin of potatoes is impermeable to water solutions, 
allowing neither salt nor water to pass through. The possibly semi- 
permeable character of cellulose membranes cannot be overlooked 
in future investigations dealing with the entrance of salts into 
plant tissues. 
5- OSMOTIC PRESSURE AND IMBIBITION FORCES 
The experiments upon Xanthium seeds with concentrated salt 
solutions suggested the possibility of measuring the capillary and 
imbibition forces of seeds by use of solutions of very high known 
osmotic pressure, since the balancing of osmotic pressure on the one 
hand against capillarity and imbibition on the other through a 
perfect semipermeable membrane is a very simple matter. 
For this purpose saturated solutions of lithium chloride, which 
