178 BOTANICAL GAZETTE [SEPTEMBER 
membrane are carefully sealed with more of the wax. leaving only 
that portion of the membrane immediately over the hole in the cork 
entirely free from wax. In my experiments the area of membrane 
left uncovered has been approximately equal to the area of the 
perforation through the cork. 
The 6 cm. glass tube is now placed in vertical position, with the 
membrane at the lower end. A.4M solution of NaCl is introduced 
through the upper cork until the chamber is quite filled. Care 
must be taken that small bubbles of air which tend to remain in the 
perforation of the lower cork while the chamber is being filled do not 
prevent the solution from filling this perforation. Otherwise the 
membrane will not be in contact with both water and solution. 
Finally a long glass tube 3 mm. in diameter is carefully inserted 
through the upper cork. The salt solution will rise a short distance 
in the narrow tube, due to displacement. After making sure that 
the apparatus is entirely free from salt solution externally, the 
chamber is suspended in a vessel of distilled water with the liquids 
at the same level, just as if it were a thistle tube. This apparatus 
and the experiment itself are so simple that they should be of con- 
siderable pedagogical interest, as demonstrating directly the inde- 
pendence of semipermeability of this kind from any vital, matter. 
In one such experiment a rise of 175 mm. occurred in the narrow 
tube in 7 days. This is a fairly rapid rise, inasmuch as the tube in 
which the rise was measured had practically the same cross-section 
area as the diffusion membrane. It means that on the average a 
column of water 2 5 mm. long passed through the membrane in a 
day’s time. The rate of passage is so rapid as to indicate a very 
slight resistance of the membrane to the passage of water, a condi- 
tion quite different from that found in the Gramineae, as already 
suggested. 
Here again the impermeability of the membrane was demon- 
strated by dropping some of the liquid taken from immediately 
below the diffusion membrane into AgNO,;. No visible pre- 
cipitate was obtained, even at the end of 7 days. 
3- STRUCTURE AND COMPOSITION OF THE TESTA 
The morphological development of the seed coat of Xanthium 
has not been fully traced, but it is probable that the seed coat Is 


