ORGANIZATION OF VOLKMANNIA DAWSONI. 35 



the conclusion. It does not follow from this, however, 

 that all the Asterophyllites and Annularis are Calamitean. 

 It is possible that, as Dr. Dawson contends, there may be 

 amongst these verticillate types of foliage one group 

 belonging to Calamites and another to some other class of 

 plants more nearly allied to the Terns. If this latter pos- 

 sibility be converted by further discoveries into an un- 

 questioned fact, we shall have two groups of verticillate- 

 foliaged plants amongst which to find those of which our 

 strobili are the fruits, viz. a section of the Asterophyllites 

 and the genus Sphenophyllum. 



When we compare the internal organization of the fruits 

 themselves, we discover that we now possess three very 

 distinct kinds, but two of them may, notwithstanding 

 generic differences, belong to allied types, if not to the 

 same. 



In the fruit which I previously described, and to which 

 reference was made at the beginning of this memoir, the 

 structure of the central axis is almost exactly that of a 

 Calamitean stem, even in its minuter details. In each 

 there is a central cavity lined with cellular tissue and sur- 

 rounded by a woody zone consisting of a ring of woody 

 wedges, each of which has a longitudinal canal at its inner 

 border ; and this zone, in turn, is invested by a second cel- 

 lular laver which in the true stem becomes a well-defined 

 bark or dermal layer, but which in the axis of the fruit is 

 not capable of being distinguished, the three tissues being 

 there more intimately blended into one than in the stem. 

 The great point upon which I wish to insist is, that the 

 arrangement of these tissues in the axis of the fruit referred 

 to and in the Calamitean stems is so identical, that no rea- 

 son whatever can be shown why the former should not have 

 been the terminal prolongation of one of the latter. 



But when we come to the other two types, viz. that 

 which both Mr. Binney and Mr. Carruthers have identified 



d2 



