Plants in their Relation to Others. 
505 
received their floras was by land and not by casual oversea transport, and it 
will also show that the distribution accorded in general with the rule of Age 
and Area, and that the endemic genera in general are young genera in their 
early stages, and not survivals. 
In order to arrive at a result which cannot be the subject of cavil on 
account of incompleteness, I have included in the present paper all the 
endemic genera of all the islands in the world, amounting to 1.583, or 12-6 
per cent, of the 12,51 7 in the world. I have taken them from my Dictionary 
(4th ed., 1919), thus including many that would generally be merged in 
others, but at least getting a complete list of all that are at all frequently 
considered as separate genera. 
The three great groups of islands in the world are all in the tropics, 
and one must bear this in mind in considering the composition of their lists 
of genera. A counting of the genera in each of these three groups — (1) the 
Indo-Malayan Islands, including Ceylon, the Malay Archipelago, Polynesia, 
New Caledonia, &c. ; (2) the African Islands, including Madagascar, the 
Mascarenes, Socotra, &c. ; (3) the American Islands, including the West 
Indies and Galapagos — soon shows that in all much the same families stand 
at the top of the list of genera. The following table shows the first ten 
families in each case, with the number of endemic genera belonging to 
them : 
1. Indomal. Islands. 2. African Islands. 3. American Islands. 
I. 
*fOrchidaceae 
79 
*fRubiaceae 
29 
*f Rubiaceae 
2 5 
2. 
*fRubiaceae 
67 
* Palmaceae 
27 
fCompositae 
20 
3 - 
* Palmaceae 
fAsclepiadaceae 
2 5 
*f Euphorbiaceae 
13 
4 - 
*fEuphorbiaceae 
38 
fAcanthaceae 
2 4 
*f Leguminosae 
13 
5 - 
Araliaceae 
26 
fCompositae 
22 
* Palmaceae 
13 
6. 
Melastomaceae 
23 
*fOrchidaceae 
19 
*fOrchidaceae 
12 
7 - 
Anonaceae 
19 
*fLeguminosae 
15 
fAcanthaceae 
8 
8. 
*fLeguminosae. 
19 
Sapindaceae 
14 
fAsclepiadaceae 
7 
9 - 
Sapindaceae 
J 9 
*fEuphorbiaceae 
13 
Apocynaceae 
6 
10. 
Apocynaceae 
17 
Bignoniaceae 
10 
fGramineae 
6 
* In all three lists. f In the first ten largest families of the world. 
This table, incomplete though it be, does not offer any suggestion that 
the endemics of the islands are survivals. There are only seven families in 
all that do not come into the first ten in the world : of these Palmaceae, 
Melastomaceae, Sapindaceae, and Apocynaoeae are found in the second ten, 
and of the rest Bignoniaceae are twenty-second in the world with 119 genera, 
Anonaceae twenty-sixth with 108, and Araliaceae thirty-ninth with 81. 
The enormous majority of the endemic genera of islands belong to the 
three island groups just mentioned, and when one adds up the grand total 
for all islands in the world one arrives at the following table : 
