438 



Mr. R. Mailet on Volcanic Energy. 



[June 20, 



produces no increase in the number of the woody wedges, but that each 

 one of the latter enlarges by successive additions to its peripheral portions 

 of new laminse, which latter partly fill up the increasing area of the en- 

 larging circle, and partly encroach upon the primary medullary rays, as 

 represented in my figure 17, in addition to some interstitial growth. 



We thus learn that as the ligneous cylinder of a Calamite increased in 

 age and size it gradually exhibited less and less of the Calamitean pecu- 

 liarities seen in young stems ; its external portions assumed a generalized, 

 unsulcated form, which recurs with remarkable uniformity in several other- 

 wise different plants of the Coal-measures. 



Amongst the Burntisland fossils sent to me by Mr. Grieve, I find two 

 very curious stems, probably of the same general nature as Zygopteris. 

 Both have a dense outer cortical layer, with vascular bundles in the inte- 

 rior. In the simpler of these plants~the transverse section of this bundle is 

 crescentic ; but in the concave border of the crescent are two small project- 

 ing capes dividing it into three minor bays (fig. 2). In the other the vascular 

 axis is a double one, lodged in a somewhat elliptical stem : one of these is a 

 simple crescent, the concavity of which is directed inwards ; the other has 

 a very elegant transverse section (fig. 1 ). It is shaped like a dumb-bell, one 

 head of which rests within the concavity of the crescentic bundle, and the 

 other turns in the opposite direction ; at each of these two extremities the 

 margin of the dumb-bell is excavated into a small bay, as if a vertical canal 

 had existed at each point ; but these seem to have been merely columns of 

 cellular tissue encroaching upon the rounded outline of the vascular struc- 

 tures. I propose provisionally to recognize these two forms under the 

 generic name of Arpexylon* 



Fig. 1. Arjpcxylon duplex. Fig- 2. Arpcxylon siwphx. Fig. 3. Edraxyhn. 

 Fig. 3 represents a stem or petiole in which the section of the vascular bundle pre- 

 sents the form of a chair or seat, and to which I propose to assign the name 

 Edraxylon. This form exhibits numerous modifications of the pattern represented 

 in the outline down to a single central vascular bundle. It may prove to belong to 

 Diet yoxy Ion Oldhamhim . 



VII. "Volcanic Energy: an attempt to develope its true Origin and 

 Cosmic al Relations." By Robert Mallet, F.R.S. Received 

 May 13, 1872. 



(Abstract.) 



The author passes in brief review the principal theories which in modern 

 times have been proposed to account for volcanic activity. 



