460 MR. H. B. GUPPY : PLANT-DISTRIBUTION 
the differentiation of the climatic zone is the most typical of all, making a 
near approach to the Dicotyledons in their entirety and the nearest of all to 
the Angiosperms in the mass (Table V.). 
Comparison may now be made between the Monocotyledons and the 
Sympetale as representing the extremes of the series constituted by the six 
primary groups. It has been shown in an earlier page that with regard to 
the detachment or differentiation of temperate floras from the original 
tropical flora the Dicotyledons are far in advance of the Monocotyledons. 
But, as indicated in the columns of Table V., the five groups of the 
Dicotyledons exhibit considerable divergencies in their behaviour in this 
respect ; and it is not possible to construct a series with the Monocotyledons 
and the Sympetale at the extremes, Yet in view of the position of these 
two groups at the extremes of the series accepted by some systematists, 
a brief comparison may be profitable. The escape of the Sympetalie from 
the tropies, as contrasted with the lagging behind of the Monocotyledons, is 
illustrated in different fashions in the columns of Tables IV., V., and VII. 
Nearly all the tropical families of the group last named, that is 23 out of 25, 
are exclusively tropical. With the Sympetale only 14 out of the 25 
tropical families are exclusively tropical. Then, again, whilst 12 out of the 
43 families of the Monocotyledons are fairly well shared between the tropical 
and temperate zones, with the Sympetale the number of families shared is 
4out of 51, or only about 8 per cent. The bulk of the non-tropical families of 
the Monocotyledons are in fact in the transition state. With the Sympetalie 
the non-tropical families have in most cases reached a further stage and 
are more or less completely detached from the tropics. Whilst with the 
Monocotyledons the families exclusively tropical amount to 53 per cent. 
und those exclusively or mainly temperate to only 14 per cent., with the 
Sympetale only about 27 per cent. of the families are confined to tropical 
regions and as many as 43 or 44 per cent. are exclusively or mainly 
temperate. A possible explanation of the contrast in behaviour between 
these two groups is supplied in the great predominance of families of 
aquatic habit in the Monocotyledons (see Table V.); but this is a matter 
discussed in the following note. 
Note on the influence of aquatic and sub-aquatie families on the distribution 
of the Angiosperms. 
The apportionment of the families of aquatic habit between the larger 
groups of the Angiosperms and their distribution over the eastern and 
western hemispheres are illustrated in Tables V. and VI. Of the 26 aquatic 
families recognized by the writer, 13, or half, are appropriated by the 
Monocotyledons, 12 belong to the Archichlamydew, and only 1 to the 
Sympetala, namely the Lentibulariaceæ. It has been shown that it makes 
