THE DESCENT THEORY CONFIRMED, II5 
other families, the extensive division of the Lip-blossoms 
(Labiatze) 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 Gamopetalze appear in the organic history of 
the earth later than all the main groups of the vegetable 
kingdom—in fact, not until the ceenolithic 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 confirmation 
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. will clearly show. During 
the whole of the long primordial period there existed only 
the lowest and most imperfect group, that of the Algz. 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 only 
