VIl] NEMATOPHYCUS. 201 



to afford distinct evidence of the original existence of such 

 walls. The figures accompanying the description do not carry- 

 conviction as to the correctness of the reference of the tubes to 

 imperfectly preserved sieve-hyphae. 



The following list, taken, with a few alterations, from 

 Penhallow's memoir', shows the geographical and geological 

 range of the species of Nematophycus hitherto recorded. 



{Lower Devonian of Gaspe. 

 Silurian [Wenlook] of England. 

 Silurian of New Brunswick. 

 N. Eicksi rEth.) Silurian (Wenlock) of N. Wales. 



N. crassus (Daws.)^ Middle Devonian of Gasp6 and New 



York. 

 N. laxus (Daws.) Lower Devonian of Gasp^. 



N. tenuis (Daws.) Lower Devonian of Gasp^. 



N. Storriei (Barb.) Silurian (Wenlock) of Wales (Cardiff). 



N. dechenianui (Pied.) Upper Devonian of Germany (Graf- 



rath). 

 N. Ortoni (Pen.) Upper Erian of Ohio. 



In summing up our information as to the structure of 

 Nematophycus we find there are certain points not definitely 

 settled, and which are of considerable importance. The few re- 

 corded instances of spore-like bodies by Penhallow and Barber 

 are not satisfactory ; we are still ignorant of the nature of the 

 reproductive organs. Such instances of lateral appendages as 

 have been referred to do not throw much light on the habit of 

 the plant. So far as we know at present the stem of Nema- 

 tophycus was not differentiated internally into a cortical and 

 central region. It may be that the specimens have been only 

 partially preserved, and the coaly layer which occasionally 

 surrounds a stem may represent a carbonised cortex which has 

 never been petrified. The large and loosely arranged tubes 

 constitute the chief characteristic feature of the genus ; in 

 some cases {N. Logani) there is an accompanying plexus of 

 smaller hyphae, in others {N. Storriei) there is no definite 

 division of the tissue into two sets of tubes of uniform size, and 

 in N. Ortoni the tubular elements are all of the large type. 



1 Penhallow (96) p. 47. 



" Carruthers (72) p. 162 regards this species as identical with N. Logani. 



