1484 CLASSIFICATION AND SUCCESSION OF PLANTS. 



the type of a special group, for which he has proposed the name of 

 Nematodendrece. The same authority is of opinion that the minute 

 globular bodies to which the name of Pachytheca has been given, 



Fig. 1357. — a, Trunk of Ne7tiatophyton (Prototaxites) Logani, 18 inches in diameter, as seen 

 in the cliff near L'Anse Brehaut, Gaspe ; B, Two of the tubular cells forming the tissue of the 

 stem, highly magnified. Lower Devonian, Canada. (After Dawson.) 



may perhaps have been the fruit of Nematophyton. As previously 

 noted, the genus occurs also in the Silurian rocks. 



Coming to higher plants, the Rhizocarps are represented in the 

 Devonian flora by such types as Sphenophyllum and Psilophyton, 

 the latter showing affinities with the Lycopods. Moreover, some of 

 the Devonian shales of North America are crowded with minute 

 globular thick-walled bodies (fig. 1358), of a diameter of one- 

 hundredth of an inch or more, which Dawson regards as being 

 probably of the nature of the " macrospores " of plants allied to 

 the Rhizocarps. These were originally described under the name 

 of Sporangites Huronensis, but they are now referred by Dawson 

 to the provisional genus Protosalvinia. Similar bodies have been 

 shown to occur, often in vast numbers, in shales of Carboniferous 

 age in both North America and Europe, and even some coals 

 appear to be largely made up of structures of a similar nature. 



Of still higher groups of plants, the Devonian rocks have yielded 

 the remains of Lepidodendron and Sigitlaria, representing the Lyco- 

 pods, and of early types of Calamites, representing the Horsetails ; 

 while true Ferns, some of which attain considerable dimensions, are 



