EVOLUTION 



393 



perish as a result of being handicapped in competition against, 

 either their more adaptable contemporaries, or new forms which 

 were better equipped to withstand the changed environment. 

 The evolutionist conceives of all life as having developed 



Fig. 229. — Seedling of an Acacia, showing the gradual differentiation of 

 phyllodes, and suppression of the laminae, in leaves of successive ages. 



from relatively simple undifferentiated unicellular organisms, 

 many of whose descendants, through the ages, have gradually 

 acquired an increasing complexity of structure in relation to 

 progressive division of labour. On this hypothesis, if our know- 

 ledge of all the extinct plants of former eras were complete, we 



