

1917] 



DENN Y—PERMEA BILI T I 



393 



rate of penetration will be dealt with in a later paper. It may be 

 stated here, however, that thickness of membrane is not the limiting 



factor. The 

 thickest is th 



memb 



is that of Cucurbit a, and the 



TABLE XVI 

 Relative permeability of various membranes 



Membrane 



Water (in 



mg.) passing 



through 



per hour 



Citrus grandis 



u 

 it 



a 

 u 

 a 



Cucurbita Pepo 



« u 



u 



it 



a 

 tt 



u 



maxima 



a 



a 



Xanthium pennsylvanicum 



a 

 a 



a 



u 



u 

 a 



* * 



Juglans regia 



« a 



Allium Cepa 



Membrane 



Allium Cepa 



.. 



a 



a 

 u 



Prunus Amygdalus dulcis 



u 

 u 

 a 



u 

 u 



a 



u 

 u 

 u 

 



u 

 u 



Arachis hypogaea 



u a 



u 

 u 

 u 

 u 

 u 



a 

 u 

 u 

 a 



Dioon edule 



Water (in 



mg.) passing 



through 



per hour 





39-2 

 12.9 



12.3 



31.2 



22.4 



120.0 



144.0 



72.0 



86.0 



60.0 



72.0 



72.0 



328.0 



53° -o 

 564.0 



710.0 



528.0 

 672.0 

 584.0 



777-5 



Structures of membrane used 



The layers of tissue represented in the ripened seed coat of the 

 various species and their origin have not been accurately determined 

 by an examination of successive stages of the development of the 

 seed. A study of the histology of the seeds of Cucurbita has been 

 made by Barber (2), of Prunus Amygdalus by Pechoutre (23), of 

 Xanthium by Haxausek (15), of the Leguminosae by Pammel (22), 

 and of the seed coats of various species in many families by Lonay 

 (20), Brandza (7), Guignard (w), and Harz (17). From an 

 examination of sections of the membranes used, and from a 

 comparison made with the reports of these investigators, it is 

 believed that the following structures are involved in these mem- 

 branes: (1) an outer integument, a much compressed and hardly 





