DISTRIBUTION OF THE MORE PEOMINENT NATTJEAL OEDEES. 251 



plants*, and that of St. Helena 26*3 per cent. Mr. J. Ball states f that in a small 

 collection made by him in the upper valley of the Eimac, on the Peruvian Andes, the 

 Compositae amounted to nearly a quarter of the whole; and he continues: — " But the 

 proportion in my list for the higher or alpine region is a full third of the whole, and, 

 as far as I can judge, this is not far from the truth for the Andes of Peru and Bolivia." 

 But these very high percentages are only obtained where the flora is relatively poor 

 in species ; and certain parts of the Mexican region would doubtless yield similar 

 results. Ball says that the proportion of 25 per cent, of Compositae seems to prevail 

 throughout the temperate regions of South America. We find by a rough calculation 

 of the pages occupied by the Compositae in Philippi's catalogue of the plants of Chili, 

 that they form about 19*5 per cent, of the phanerogams; a higher proportion than we 

 had expected. The only large area of which there are published data for comparison 

 is Australia. Baron Mueller J makes the total number of Australian phanerogams 

 8566, and the Compositae 535, which gives a percentage of 6*2. In South Africa the 

 Composite are proportionately much more numerous ; and the " Composite Region " of 

 Bolus §, a central area of 4000 to 5000 feet elevation sloping towards the Orange River, 

 is especially so, amounting to 23*6 per cent. But the great abundance of the Com- 

 positae is only fully realized when we know that the order next in predominance, the 

 Gramineee, only reaches 8 per cent. ; and we are told that the preponderance of 

 individuals is immensely in excess of the numerical proportion of the species. Unfor- 

 tunately there are almost no published data respecting individual development in the 

 Mexican flora. 



A brief analysis of the composition and distribution of the Compositae of the Mexican 

 flora must terminate this general sketch. 



Eleven out of thirteen of the suborders are represented ; the other two, the Calen- 

 dulaceae and Arctotideae, are confined to the Mediterranean region and Africa, and 

 almost exclusively to South Africa, where they number 320 species. The essentially 

 American Helianthoideae have their greatest concentration in Mexico and amount 

 to 32 per cent, of the species and two fifths of the genera of the whole of the 

 Compositae of the region. Twenty-three of the genera and 400 of the species are 

 endemic ; and fifty of the remaining genera are restricted to America, thus leaving 

 only twelve that extend beyond America ; and only three of the species inhabit other 

 countries. The average number of species to each genus is only about 5*7, and the 

 only large genera are Verbesina, with forty-one species, and Zexmenia, with twenty- 

 nine species. Numerically, in species at least, the Eupatoriaceae come next to the 

 Helianthoideae, the number of genera being only a quarter as many. A third of the 



* 'Challenger' Expedition, Botany, i. 2, p. 54, and 3, p. 19. 



t Journ. Linn. Soc. xxii. p. 10. 



% Systematic Census of Australian Plants. Third Annual Supplement, 1886, p. 6. 



§ Sketch of the Elora of South Africa : Official Handbook to the Indian and Colonial Exhibition, 1886, p. 313. 



biol. cente.-amee., Bot. Vol. IV., August 1887. 2 I 



