MB. G. BENTHAM ON EUPIIORBIACE^. 249 



bia eremophila may be cited as instances of that apparently very 

 ancient but long-interrupted connexion referred to in my Notes 

 on Composite, p. 553. 



The great genus Euphorbia, when it first spread into America, 

 must have already acquired the remarkable fixity in the essential 

 characters of the flower-head, and have already proceeded to 

 some further differentiation continued in different directions in 

 the two continents. Besides the common section Anisophyllum, to 

 which I shall presently recur, we have three great groups, chiefly 

 characterized in the Old World and scarcely known in tropical 

 America: — 1. Eremophyton, perhaps the oldest, comprising about 

 seven tropical African or West- Asiatic species, and one Austra- 

 lian offset (the above-mentioned E. eremophila), with a dichoto- 

 mous or irregular ramification, without having acquired any of the 

 peculiarities distinguishing the other sections. 2. Euphorbium, 

 about a hundred species, more or less succulent and leafless (an 

 adaptive character, the probable result of their spread over the 

 succulent-bearing regions of the Old World), not extending north 

 of Africa, but abundant in southern as well as in some parts of 

 tropical Africa, and represented (in its subsection Tirucalli in- 

 cluding Arthrothamnos) by two West-Indian and perhaps by one 

 North-Chilian species. And 3. Tithymalus, with leafy stems and 

 umbellate upper flowering branches — a vast group which app 

 to have originated in some part of the Mediterranean region, 

 where many of its races now luxuriate in the highest state of pros- 

 perity and variability, and whence it has spread over Europe and 

 a great part of Asia, and may have reached America by a route 

 north of the tropics. Out of the 310 admitted species, 48 are 

 American and almost all northern and extratropical, about 12 

 extratropical South-African; the remaining 250 belong to the 

 Mediterranean and north temperate Old- World regions, or only 

 reach the tropics in mountain regions north of the equator. 



In America the genus has taken a different course. Eremo- 

 phyton is there replaced by Adenopetalum, a series of about seventy 

 species, exceedingly diversified in habit, some not unlike corre- 

 sponding Old- World species of Eremophyton or even of Euphor- 

 bium, some with a habit unknown in the Old World, and all as- 

 suming a specially American character, the development of a 

 petal-like appendage on the back of the involucral glands. Again, 

 Poinsettia is another specially American divergence from the 

 primitive type The involucre remains without petal -like appeu- 



