SUEVIVALS AMONG PLANTS OF THE PAST. 



307 



SUEVIVALS AMONG PLANTS OF THE PAST. 

 By Eev. Professor G. Henslow, M.A., V.M.H., (^c. 

 [Read June 7, 1910.] 



Ea^olution as popularly understood is supposed to imply a gradual 

 improvement in the structures of animals and plants, as developed 

 through the past ages of the world, until the most perfect type of all, 

 Man, closed the series. This is true in a sense, but it must be borne 

 in mind that each and every kind was, and is, as perfectly adapted to its 

 position in Hfe as it requires to be. The advancement is perhaps best 

 seen in the fact that the adnlt forms of the earlier ages corresponded 

 with the young or embryonic stages of later and existing types of the 

 same groups. Thus the " tadpole and newt " stage of the Amphibia 

 were the highest attained in the period when coal plants grew; the frog 

 type is of a much later origin. 



But each group had its day and then died out ; so that, as a rule, it is 

 only organisms of the latest geological eras that still exist. Yet a 

 certain number of types of several ancient groups are represented at 

 the present day, if not by identically the same species, by some more 

 or less closely allied specific forms of the same genus ; or it may be 

 that a different genus now stands for its ancient and extinct forebears. 



Thus, one of the oldest shells known, the impressions of which are 

 found on slates near the top of Cader Idris, in Wales, was apparently just 

 like the Lingula of to-day. The Nautilus, or type genus of the great 

 family Nautilidae, which succeeded the Lingula in a subsequent period, 

 is the sole generic survival ; while the vast number of Ammonite's, which 

 were evolved out of the Nautilidae, are gone for ever. 



Similarly among plants survivals are still with us, and I purpose 

 selecting some of the more interesting and better-known examples out 

 of the great groups or classes of plants knowm as the higher Crypto- 

 gams, Gymnosperms, and Angiosperms, which last include Dicotyle- 

 dons and Monocotyledons. 



As far as is known, only the first two have been found in the earliest 

 or Primary strata, which ended with the Goal period, and in a stratum 

 which covered them (Permian). The Secondary epoch ends with the 

 Chalk. In the Secondary strata are found types which more resemble 

 those of living forms. The Tertiary epoch begins with the Eocene 

 strata — i.e. " Dawn of the New " periods. In these we begin to feel 

 at home among the later fossil floras, especially in the next stratum 

 or Miocene. 



Turning to living groups of the higher and woody-stemmed Crypto- 

 ganis, those more or less represented among coal plants are the Horse- 



