EVOLUTION 397 



The brief review of the groups here given is sufficient to 

 indicate that the extinct Clubmosses and Horsetails, in the era 

 of their success, were more specialised and more complex than 

 their present descendants, which play so subordinate a role, and 

 probably owe their survival to features which characterised 

 the less successful members of these groups in the past. Such 

 considerations lead one to suspect that the subordinate groups 

 and individuals of any one age are the most likely starting-points 

 for the dominant vegetation of the next, and so we can understand 

 why the fossil record presents us with abundant examples of 

 clearly defined groups {i.e. of the prevalent successful forms) and; 

 comparatively few representatives of groups " in the making."'. 

 Indeed, the fossil plants of past ages and the living organisms' 

 of to-day combine to emphasise the rarity of the " missing link " 

 which, like the thinker in advance of his age, is not sufficiently 

 in harmony with the environment to command success, buti 

 yet marks the beginnings of the fades of the future. It is not, 

 therefore, surprising that our progress in the reconstruction. 

 of the genealogical tree of the Vegetable Kingdom is slow, and , 

 that many of the groups remain in striking isolation from one 

 another. 



