1917] DENNY— PERMEABILITY 479 



dilute acids and bases. The cells themselves are filled with fatty- 

 substances that are only partly removed by extraction with lipoid 

 solvents. Even after 18 hours of extraction lipoids may still be 

 detected in the coat. 



In these various experiments the grapefruit seed coat differed 



from all others in failing to show increased permeability, or at 



least a readable rate of water movement after any of the methods 



of extraction. All tests of this membrane with the osmometer 



indicated a relatively high resistance of the coat to the passage of 

 water. 



A parallel experiment was carried out to give further evidence 

 on this point. This was done by comparing the absorption of 



.... o 



d 



w 



Fig. 5. — Cross-section of seed coat of Citrus grandis, X45° 



water by the seeds, one lot with coats and the other lot without 

 coats. More than one embryo is usually found in these seeds, 

 so that when the coat is removed the embryos fall apart and 

 accurate weighings are impossible. To overcome this difficulty, 

 a narrow band of seed coat was left around the embryos. This 

 band held the embryos together so that weighings could be made. 

 Table VII shows the results obtained, and curves of these results 

 are shown in fig. 6. 



It was found that treating the grapefruit membrane with acids 

 and bases increased its permeability to such an extent that a read- 

 able rate of water movement could be obtained. Thus, soaking 

 a membrane in warm 2 per cent sodium hydroxide increased the 

 rate from o to 24.26 mg. of water per hour; and in another test 

 soaking the membrane in 2 per cent sodium hydroxide for 24 hours 

 increased the rate from o to 72.12 mg. By such treatment, how- 

 ever, the tissue of the seed undergoes a disintegration, so that the 







