THE DESCENT THEORY CONFIRMED. I I 5 



other families, the extensive division of the Lip-blossoms 

 (Labiatse) and the Composites. In these last the differen- 

 tiation and perfection of the Phanerogamic blossoms attain 

 their highest stage of development, and we must therefore 

 place them at the head of the vegetable kingdom, as the 

 most perfect of all plants. In accordance with this, the 

 legion of the Gamopetalse appear in the organic history of 

 the earth later than all the main groups of the vegetable 

 I kingdom — in fact, not until the csenolithic or tertiary epoch. 

 In the earliest tertiary period the legion is still very rare, 

 but it gradually increases in the mid-tertiary, and attains its 

 full development only in the latest tertiary and the qua- 

 ternary period. 



Now if, having reached our own time, we look back upon 

 the whole history of the development of the vegetable 

 kingdom, we cannot but perceive in it a grand confiritnation 

 of the Theory of Descent The two great principles of organic 

 development which have been pointed out as the necessary 

 results of natural selection in the Struggle for Life, namely, 

 the laws of differentiation and perfecting, manifest them- 

 selves everywhere in the development of the larger and 

 smaller groups of the natural system of plants. In each 

 larger or smaller period of the organic history of the earth, 

 the vegetable kingdom increases both in variety and perfec- 

 tion, as a glance at Plate IV. wiU clearly show. During 

 the whole of the long primordial period there existed only 

 the lowest and most imperfect group, that of the Algae. To 

 these are added, in the primary period, the higher and more 

 perfect Cryptogamia, especially the main-class of Ferns. 

 During the coal period the Phanerogamia begin to develop 

 out of the latter ; at first, however, they are represented onlv 



