Manchester Memoirs, Vol. xlvi. (1902), No. 9. 3 



at the centre, so that he arrived at the conclusion that 

 Stiguiaria possessed a " fistular medulla," though he often 

 found thin layers of pith cells lining the vascular cylinder 

 and in continuity with the primary medullary rays. 

 Scott,* too, speaks of the pith being rarely preserved, 

 except in the outer part, and possibly of a fistular nature. 

 The presence in XenopJiyton of such a well-defined 

 medullary tissue might be due {a) to the age of the speci- 

 men, {b) to the state of preservation, or {c) to a specific 

 difference between Xenophyton and other Stigmarice. 



{a) It might be argued from the persistence of the pith 

 that our Xenophyton specimen was a young Stigniaria, in 

 which the fistular character of the pith had not yet been 

 developed. But the size of the specimen is greater than 

 that of many Stigmarice, which have a hollow pith, so that 

 we have no reason, from its size, of supposing it to be a 

 young " root." The small amount of secondary wood 

 might possibly be taken as indicative of its youthful 

 condition, but I am inclined to look upon this as a 

 specific difference of this specimen. The presence of a 

 well-marked periderm, as well as the bulk of the specimen, 

 incHne me to the belief that we have to do with a mature 

 specimen. 



ib) As regards the state of preservation of the 

 specimen, the presence of an extraneous stigmarian 

 rootlet outside the central vascular cylinder, and even 

 burrowing into the pith (as in the section figured in the 

 present paper), indicate that the specimen must have 

 been exposed to some destructive changes before fossiH- 

 sation, so that the preservation of the pith in our specimen 

 would point to a considerable durability of this tissue. 



ic) As in the specimen before us, then, we have the 

 pith well preserved in what we must regard as a mature 

 * Scott, D. H. ("oo) p. 222. 



