270 MORPHOLOGY OF ANGIOSPERMS 



Cajipanales. — The Cucurbitaceae are tropical ; the Cam- 

 panulaceae belong to the north 'and south temperate regions, 

 with the lobelias as tropical representatives; the Goodeniaceae 

 and Candolleaceae are Australian; the Calyceraceae are mainly 

 tropical American; and the Compositae are world-wide in their 

 distribution. 



The main conclusions to be derived from the above facts are 

 as follows : 



1. The Sympetalae as a whole are better defined geograph- 

 ically than the Archichlamydeae. This probably follows from 

 the fact that they are better defined structurally. 



2. There is a much more even distribution between the 

 tropics and temperates than among the Monocotyledons and 

 Archichlamydeae. Of course the tropical display is the larger, 

 but it is hardly more than might be regarded as the normal 

 ratio of increase in passing from the temperates to the 

 tropics. 



3. The Sympetalae as a whole, the youngest of the Angio- 

 sperm groups, seem to have become prominently adapted to the 

 relatively unoccupied temperate and boreal conditions, and to 

 have made in them their most characteristic display. From 

 this general point of view, the Monocotyledons and Archi- 

 chlamydeae are characteristically tropical, and the Sympetalae 

 as characteristically temperate. 



4. There is a remarkable paucity of aquatic forms as com- 

 pared with Monocotyledons and Archichlamydeae. This is 

 probably associated with at least two facts — namely, the lack 

 of primitive angiospermous types among the Sympetalae, and 

 the previous occupation of the water conditions by the older 

 Monocotyledons and Archichlamydeae. 



5. The Sympetalae show no such notable continental pair- 

 ing as is characteristic of the Archichlamydeae. It would seem 

 that this may lie related to the temperate and boreal develop- 

 ment of the group, which would retain continental connections 

 much longer than would be possible for a group of more tropical 

 tendencies. 



ii. The dominance of America in the tropical displav of 

 Sympetalae is almost as notable as among the Archichlamvdeae. 

 The excessive rainfall is doubtless one factor in the explana- 

 tion, lint whether ii is the chief one is uncertain. 



