ON THE MORPHOLOGY OF PINITES OBLONGUS. 189 



former paper^ we have V= ^-^^ = 677 feet per second, 



or approximately one half the velocity due to the height 

 of the homogeneous atmosphere. 



The following approximate velocities with which atmo- 

 spheres of several gases of 15 lbs. absolute pressure rush 

 into a vacuum through an orifice of the best form, before 

 expansion, have been calculated on the basis of Graham^s 

 law of the velocities of eflSux for equal pressures being 

 inversely as the square roots of the specific gravities : — 



Air I'ooo X 677 = 677 feet per second. 



Oxygen o'95o X 677 = 643 „ „ 



Nitrogen i-oi5 X 677 = 687 „ „ 



Hydrogen 3-800 X 677 = 2572 „ „ 



Saturated steam... i'445 X 677 = 978 „ „ 



XIII. On the Morphology of Pinites oblongus (Abies 

 oblonga of Lindley and Button) . By Wm. Crawford 

 Williamson, LL.D., F.R.S., Professor of Botany in 

 Owens ColleffC. 



Eead April 6th, 1886. 



(Plate IX.) 



The question of the range of the Coniferse in time, and 

 its important bearing upon the problem of evolution, 

 sufficiently accounts for the interest attached to the dis- 

 covery of cones belonging to that order in the various 

 stratified rocks. Several such have already been met 

 with, but amongst these a few objects have been obtained 

 from the Palaeozoic and other Mesozoic rocks that are 



