192 THALLOPHYTA. [CH. 



futility of relying on imperfectly preserved external features as 

 taxonomic characters of primary importance. 



An example of a supposed Jurassic Fucus is shown in fig. 49, 

 and briefly described in the Chapter dealing with fossil Bryo- 

 phytes. 



Several species of Flysch Algae have recently been referred 

 by Rothpletz^ to the Phaeophyceae under the provisional 

 generic name Phycopsis, but they are of no special botanical 

 interest. 



The extremely interesting genus Nematophycus has lately 

 been assigned by a Canadian author ^ to a position in the 

 Phaeophyceae. Although the particular points on which he 

 chiefly relies are not perhaps thoroughly established, there 

 are certain considerations which lead us to include Nemato- 

 phycus as a doubtful member of the present group of algae. 



Nematophycus. 



The stem attains a diameter of between 2 and 3 feet in the 

 largest specimens ; it is made up either of comparatively wide 

 and loosely arranged tubes pursuing a slightly irregular vertical 

 course accompanied by a plexus of much narrower tubes, or of 

 tubes varying in diameter but not divisible into two distinct 

 types. Rings of growth occur in some forms but not in others. 

 R-adially elongated or isodiametric spaces occur in the stem 

 tissues in which the tubes are less abundant. 



Reproductive organs unknown, with the possible exception 

 of some very doubtful bodies described as spores. 



In 1856 Sir William Dawson proposed the generic name 

 Prototaxites for some large silicified trunks discovered in the 

 Lower and Middle Devonian rocks of Canada. A few years 

 later the same writer'^ published a detailed account of the new 

 fossils and arrived at the conclusion that the Devonian stem 

 showed definite points of affinity with the recent genus Taxus, 

 and the generic name suggests that he regarded it as the type 

 of Coniferous trees belonging to the sub-family Taxineae. The 



1 Kothpletz (96). ^ Penhallow (96) p. 45. ^ Dawson (59). 



