T CONOCE NM 
FROM THE STANDPOINT OF AN IDEALIST. 455 
far as the principle of differentiation is concerned they behave conformably 
with their position in the differentiating scale just above the families. 
Before one proceeds to deal statistically with the large groups of the Angio- 
sperms that lie behind the cohorts, a word may be said regarding the needs 
of the differentiation hypothesis in this respect. Between the 45 cohorts 
and the two classes of the Monocotyledons and Dicotyledons, there is a con- 
siderable break or gap in the differentiating scale, which cannot be very 
satisfactorily bridged over by dividing up the Dicotyledons in a few groups 
as is done below. The advocate of the differentiation theory, and the writer 
ventures to think that his need is also that of the systematist, requires an 
intermediate group holding about a score or two dozen great alliances, each 
of them cosmopolitan or pantropical, and all families of restricted range will 
have to be reduced to terms of an alliance. Here geographical considera- 
tions would be foremost, and the complemental families as above described 
would take a prominent part in building up an alliance which would either 
possess the tropics or hold the world, the pantropical and cosmopolitan 
alliances being regarded as of equal value, notwithstanding the failure of the 
first-named to respond to the differentiation of the temperate zone. The 
object would be to restore the original world-ranging generalized types ; 
and if the number of such great alliances should exceed the limits above 
named, they would serve to displace the cohorts which could then be very 
well dispensed with. One would commend the use of familiar designations 
for all the alliances, such as Compositee, Rubiacez, Ericales, Leguminose, 
Seitaminez, Aroideze, Palme, ete. But in restoring the original type in the 
shape of an alliance we should give it the name of the tropical parent form 
where a cosmopolitan alliance is concerned. Any names like Geraniales 
and Primulales that would seem to credit the alliance with an origin in the 
temperate zones should give place to the name of the older tropical forms. 
The Monocotyledons and Dicotyledons.—N otwithstanding the great disparity 
inthe number of families they hold (Monocotyledons 43, Dicotyledons 229), 
some interesting comparisons can be made. In the first place, it wiil be 
worth while ascertaining how they stand to each other with reference to the 
proportion of families occurring in both hemispheres, the east and the west. 
They differ but little in this respect, since the proportion is 76'8 per cent. 
for the Monocotyledons and 69°4 per cent. for the Dicotyledons (Table II.). 
This approximation exists in spite of the circumstance that 30 per cent. of 
the Monocotyledonous families are aquatic or sub-aquatic (Table V.). Of 
the 272 families of the Angiosperms 26 are aquatic or sub-aquatic, and 
of these half (13) are Monocotyledons. It would therefore appear that as 
regards the occurrence of a family in both the Old and the New Worlds 
it behaves the same, whether monocotyledonous or dicotyledonous, or 
whether aquatic or terrestrial in habit. This independence of the proportion 
of aquatic plants is also displayed, as will subsequently be shown, by the 
