GEOGRAPHIC DISTRIBUTION OF ANGIOSPERMS 267 



sperm groups. If they are of equal value, the Archichlamydeae 

 respond more readily to geographic conditions than do the other 

 groups. We suspect, however, that they are of very unequal 

 value, and that the kind of response shown by the Archichlamy- 

 deae to changed conditions happens to concern the structures 

 used for determining families more than in the other groups. 



2. Among the Archichlamydeae no distinctly boreal family 

 has been developed, as among the Sympetalae. 



3. The great tropical family is the Leguminosae, by far 

 the largest Angiosperm family excepting the Compositae. If 

 the Mimosa forms are to be regarded as the primitive ones, it is 

 interesting to note that they are massed in tropical Africa and 

 Australia, and that it is the highly specialized Papilip forms 

 that have chiefly occupied the temperate regions. 



■i. Certain great families are characteristic of the north 

 temperate regions, usually being comparatively insignificant in 

 the tropics. These are the Polygonaceae, Caryophyllaceae, 

 Kanunculaceae, Cruciferae, Saxifragaceae, Rosaceae, Onagra- 

 ceae, and Umbelliferae. 



5. As among the Monocotyledons, aquatic forms are com- 

 mon and cosmopolitan, but this habit does not characterize 

 whole families so frequently as in the former group. The fact 

 that the aquatic habit is found chiefly among the Monocotyle- 

 dons and Archichlamydeae must be associated with the fact that 

 in these groups the most primitive Angiosperms occur. The 

 cosmopolitan character of such forms may be illustrated by 

 the Ceratophyllaceae, which with only three species extends 

 from the arctic to the antarctic regions, occurring even in Aus- 

 tralia and the Fiji Islands. 



6. There is a distinct pairing of continents especially in 

 tropical display, as was noted among the Monocotyledons, in 

 this case America usually being one member of the pair and 

 Asia or Africa the other. In this pairing, what may be called 

 the Pacific-distribution, involving Asia, the East Indies, or 

 Australia on the one hand, and the Americas on the other, is 

 particularly prominent. For example, the Amarantaceae are 

 massed in South America and the East Indies, the Lardiza- 

 balaceae in South America and southeastern Asia, the Calycan- 

 thaceae in North America and Japan, the Lauraeeae in Amer- 

 ica and Asia, the Malvales chiefly in America and Asia, the 



