1885.] Evolution in the Vegetable Kingdom. 753 
progressed with such amazing rapidity as to become the ruling 
type in the Cenomanian, or Middle Cretaceous, furnishing in that 
formation over seventy-two per cent of the total known flora of 
the globe, which is nearly as high a percentage as they attained 
at any subsequent period. Of the present flora they form less 
than sixty per cent, and doubtless their relative position in the 
fossil flora is exaggerated, owing to the failure of the myriad 
fungoid forms, existing then as now, to leave any traces in the 
rocks. 
The systematic value of the prevailing subdivision of the 
dicotyledons into monochlamydeous and dichlamydeous, and the 
latter again into polypetalous and gamopetalous, diminishes with 
the progress of research. The first of these divisions is invali- 
dated by the fact that the natural affinities are between apetalous 
and polypetalous and not between apetalous and gamopetalous 
plants, the last named division being the highest in point of struc- 
tural development. The apetalous division forms forty-five per 
cent of the dicotyledons in the Cenomanian, thirty-seven per cent 
in the Miocene and only fourteen per cent in the living flora. 
The polypetalz are fifty per cent in the Cenomanian, forty-eight 
per cent in the Miocene and forty per cent in the living flora. 
The Gamopetalz are five per cent in the Cenomanian, fifteen per 
cent in the Miocene and forty-six per cent in the living flora. 
Making all due allowance for the fact that the Gamopetalz of the 
living flora are more largely herbaceous than either of the other 
divisions, which fact, properly viewed, constitutes a strong proof 
of their greater recency, this evidence would seem quite sufficient 
to establish the order of development of the dicotyledons as here 
arranged. 
As still further confirming the general law of development in 
vegetable life, we observe the great decline of the cryptogamic 
types that predominated throughout the Palæozoic. The same 
is true to a less extent of the gymnosperms, and notably of the 
Cycadaceæ. The monocotyledons have also probably declined, 
as have the lower or monochlamydeous dicotyledons. The only 
one of all the leading forms of life of which we can positively say 
that it still preserves an upward tendency is the gamopetalous 
division of the dicotyledons, which, unless arrested by human 
agency, seems destined to form the dominant type of vegetation 
or the next geologic epoch. 
