CHAP, vi.] FOSSIL PLANTS. 187 



is that each important group of plants commences in a 

 small way, that is, its components are comparatively few, 

 simple in organization, and comparatively limited in 

 distribution ; as the group evolves, we find that the 

 number of species increases at a comparatively rapid 

 rate, the same being true of the general organization 

 and distribution in space ; this goes on until a maximum 

 of development is reached, after which there is in every 

 instance a contraction as it were, indicated by a weeding 

 out and disappearance by degrees of those species least 

 able to hold their ground in the increased struggle for 

 life, accompanied by a general deterioration in structure, 

 and narrowing of the area of distribution. From the 

 above account it will be seen that the life-history of a 

 group of plants may be diagrammatically represented by 

 a spindle-shaped figure, its base or starting-point corre- 

 sponding to the first geological evidence of its existence, 

 then gradually widening out to its maximum point of 

 development, then again contracting, becoming thinner 

 and thinner, indicating its gradual decline, until the 

 present period is reached, for although in some cases 

 the living representatives are exceedingly few in num- 

 bers, limited in distribution, and degenerate in structure 

 compared with the same group at the period of its 

 maximum of development, yet every important group re- 

 presented in a higher stage of development during some 

 earlier geological epoch has existed up to the present 

 time, although sections or natural orders belonging to 

 certain groups have geological ages ago become quite 

 extinct, and are only known to us by their fossil remains. 

 In such cases the general structure and microscopic 

 details afford the proofs of affinity. 



