FROM THE STANDPOINT OF AN IDEALIST. 461 
but little difference in the distribution of the larger family-groups in the 
eastern and western hemispheres whether they hold many or few aquatic 
families. Thus the Monocotyledons holding 30 per cent. of these families 
and the Sympetale holding only 2 per cent. are distributed in the same 
proportion over the Old and New Worlds, in each case about 77 per cent. of 
their families being common to the two hemispheres (Table II.). The 
aquatic families are therefore quite neutral in their influence on the general 
response of the Angiosperms to the great bi-cleavage of the land-mass of 
the globe. 
On the other hand, they sometimes seem to have a marked influence on 
the response made by families to the differentiation of the climatie zones. 
Thus, as shown in the previous note, the Monocotyledons lag behind the . 
Sympetale to a marked degree in the detachment of temperate families from 
the tropics ; and the implication is that since the former hold as many as 
30 per cent. of aquatic families, and the latter as few as 2 per cent., the 
influence of the aquatic habit in checking the process of differentiation 
is displayed in the diminution of the climatic contrast between the 
tropical and temperate zones. Yet, although this may sufficiently 
explain the lagging of the Monocotyledons in the tropics as compared 
with the Sympetale, it will not explain why amongst the primary groups 
of the Archichlamydez those that are most tropical, like © and D, hold 
the smallest number of aquatic families (Table V.). 
Note on the relative proportions of * both-world " families in the tropics and in 
the extra-tropical regions of the northern hemisphere. 
The statement on page 447 that 61 percent. of tropical families and 64 per 
cent. of northern extra-tropical families occur in both the Old and the 
New Worlds is based on data given in Table III. Here we are concerned 
with families purely tropical and purely northern extra-tropical. But for 
the statement that follows it the data are only partially supplied in the 
Tables, as in IV., V., etc. It is there asserted that 69 per cent. of 
exclusively or mainly tropical families and 77 per cent. of exclusively or 
mainly extra-tropical families in the northern hemisphere are found in both 
the Old and the New Worlds. But to obtain these results i& was necessary 
to eliminate the southern extra-tropical elements ; and to avoid the necessity 
of giving another complicated set of tables I have here given the data on 
which this assertion is based. They are as follows :— 
The total of 153 exclusively or mainly tropical families is made up of 120 
exclusively tropieal and of 53 tropical and north temperate families but 
mainly tropical. (In these connections it should be sta'ed that the tropies 
include the subtropics and the north temperate all the northern extra-tropical 
regions.) Of the exclusively tropical 73 and of the mainly tropical all oceur 
