676 



^. A. J U LI EN 



sand-grains. The bubbles should therefore be more properly 

 denominated air- vesicles {Jiift-blaseii) than vapor- or steam-cavi- 

 t i e s ( darnpf-pore7i . ) 



The larger vesicles, which mostly occupy the middle part of 

 the tube-wall, seem to have been produced by crowding together 



Fig. 2. — The same. X 50. Part of wall. 



and coalescence of smaller ones. The largest, which have been 

 perforated and emptied, in making the thin section, present light 

 outlines, up to 0.2 to 0.3""" in diameter, mostly elliptical, but 

 also oval, pearshaped, lenticular, triangular, or squeezed together 

 in groups, with contiguous walls flattened by pressure in direc- 

 tion tangential to the tube-wall. Even a particular vesicle may 

 vary much in size and in form of cross-section at different 

 depths, as if distorted after formation. The longer axes of the 



