90 THE GEOLOGICAL HISTORY OF PLANTS. 



more distant. They are attached by very narrow bases, and ap- 

 parently tend to lie on a plane, though they may possibly have been 

 spirally arranged. On the same slabs are rounded sporangia or 

 macrospores like those of Lepidodendron, but there is no evidence 

 that these belonged to Trochophyllum. On the stems of this plant, 

 however, there are small, rounded bodies apparently taking the places 

 of some of the pinnules. These may possibly be spore-cases ; but 

 they may be merely imperfectly developed pinnules. Still the fact 

 that similar small granules appear on the stems of the Devonian 

 species, favours the idea that they may be organs of fructification. 



The most interesting discovery, however, which results from the 

 study of Mr. Lacoe's specimens, is that the pinnules were cylindrical 

 and hollow, and probably served to float the plant. This would 

 account for many of the peculiarities in the appearance and mode 

 of occurrence of the Devonian Ptilophy ton,, which are readily ex- 

 plained if it is supposed to be an aquatic plant, attaching itself to 

 the stems of submerged vegetable remains and standing erect in the 

 water by virtue of its hollow leaves. It may well, however, have 

 been a plant of higher organisation than the Algae, though no doubt 

 cryptogamous. 



The species of PtilopJiyton will thus constitute a peculiar group 

 of aquatic plants, belonging to the Devonian and Lower Carbonif- 

 erous periods, and perhaps allied to Lycopods and Pillworts in their 

 organisation and fruit, but specially distinguished by their linear 

 leaves serving as floats and arranged pinnately on slender stems. 

 The only species yet found within the limits of Canada is Pt. plu- 

 mula, found by Dr. Honeyman in the Lower Carboniferous of Nova 

 Scotia ; but as Pt. Vanuxemii abounds in the Erian of New York, 

 it will no doubt be found in Canada also. 



III. TREE-FERNS OF THE ERIAN PERIOD. 



As the fact of the occurrence of true tree-ferns in rocks so old 

 as the Middle Erian or Devonian has been doubted in some quar- 

 ters, the following summary is given from descriptions published in 

 the "Journal of the Geological Society of London" (1871 and 1881), 

 where figures of the species will be found : 



Of the numerous ferns now known in the Middle and Upper 

 Devonian of North America, a great number are small and delicate 

 species, which were probably herbaceous ; but there are other species 

 which may have been tree-ferns. Little definite information, how- 

 ever, has, until recently, been obtained with regard to their habit of 

 growth. 



