308 JOURNAL OF THE ROYAL HORTTCTUVrURAr. SOCIETY. 



tails or EquisetuDi, the sole sui'viving genus of llie iiatin;al order, or 

 family, Equisetaceae, its ancestors having been very numerous 

 ages ago. 



The Lycopodiaceae, having five existing genera (Lycopodium, the 

 humble club-moss, and Selaginella being familiar to all), were repre- 

 sented by gigantic trees, 100 feet tall, but only of the Selaginella type; 

 the ancestry of the club-mosses is at present unknown. Ferns or Filices 

 now exist by thousands, but impressions looking exactly like, and 

 formerly thought to be, ferns are now known to be of a higher nature. 

 The most ancient tribes have but few living representatives, such as 

 Osmundaceae, of which only the genera Osmnnda (our " Eoyal Fern ") 

 and Todea exist. Another family, Marattiaceae , with four living 

 genera, was also well represented in the Coal period. Such are 

 survivals. 



It may be laid down as a general rule that where a group has only 

 one or very few living forms to represent it, this fact implies a long-lost 

 ancestry; and that if it be found fossil, it usually had a very wide 

 distribution, both past and present, over the globe, for some of the later 

 orders and genera are in this condition to-day. Thus, our Sweet Gale 

 (Myrica Gale) is found in North America, on the mountains of Asia, 

 and extends as far as China and Japan; while several species of 

 Myrica are living at the Cape of Good Hope. Myrica is also known as 

 a fossil. 



Another very general feature about fossil animals and plants is that 

 the older types of any series are " generalized " in structure in that 

 they show characters combined in one and the same genus, which 

 become subsequently typical of distinct genera of a later period. 

 Thus the names Ichthyosaurus, or "fish-lizard," and Hyaenarctos, 

 " hyaena-bear," indicate this fact among animals. 



So it is with plants ; a very common form of impression on coal- 

 shales is one of plants with wedge-shaped leaves having the veins 

 repeatedly or " dichotomously " forking. Hence the name Spheno- 

 phyllnm, " wedge-leaf." Now, this is allied to the horsetails as well as 

 to Psilotum and Tmesipteris, two living genera of the Lycopods. 

 Similarly what were formerly supposed to be ferns from the foliage are 

 now found to have naked seeds, and are therefore gymnosperms. 



Of our survivals among Cryptograms, the horsetail (Equisetuin) is a 

 conspicuous example. Though a solitary genus now, there were many 

 allies in the Coal period; and the oldest known, Archeocalamiies , more 

 nearly resembles the living horsetails than later forms of the same 

 group. 



As with Lycopods, so with Ferns, the earliest kinds, as we have 

 stated, are now represented by tribes having few genera left. Other 

 tribes of Ferns with few genera, as Schizaeaceae (three) and Gleich- 

 eniaceae (four), are found fossil in the Secondary epoch. 



With regard to Marat liaceae, tlie sporangia, unlike those of the 

 more recent and abundant living- forms, were not separate but coherent 

 into oblong or circular button-like " synaiigia." Thus Kavlfussia, only 



