244 MORPHOLOGY OF ANGIOSPERMS 



the large families being Loranthaceae with 800 species, Santa- 

 laeeae with 246, and Olacaceae with 150. In this alliance, also, 

 the cyclic perianth is for the most part petaloid, but there is 

 advancement in the general differentiation of a calyx and co- 

 rolla. For the most part, there is a syncarpous pistil of three 

 carpels, but the carpels may be two or one ; and a free central 

 placenta develops ovules without an integument or no distinct 

 ovules at all. There is much diversity within the alliance, at 

 least three distinct lines being evident ; but the rather remark- 

 able morphological structures found in the alliance are prob- 

 ably related to their general parasitic or semi-parasitic habits. 



XII. Aristolochiales. — This includes the Aristolochia- 

 ceae, Rafflesiaceae, and Hydnoraceae, together containing about 

 235 species, of which 205 belong to the Aristolochiaceae. The 

 members of this series are distinctly in advance of the preceding 

 in the coalescence of the petaloid segments of the perianth, and 

 especially in epigynv. The indefinite number of ovules is also 

 a distinguishing feature. 



The preceding twelve alliances represent a primitive com- 

 plex, in which reduced forms may have been included. How 

 they may be related to one another in origin is too obscure for 

 profitable discussion, but it seems probable that they are not at 

 all related to the following alliances. In other words, whether 

 they represent a single genetic stock or several, they appear to 

 be isolated from the higher alliances. 



XIII. Polygonales. — This includes the single family 

 Polygonaceae, with about 750 species. Its mostly cyclic 

 flowers, with undifferentiated perianth or distinct calyx and 

 corolla, puts it upon about the plane of advancement attained 

 by the preceding alliances ; while its strong trimerous tendency 

 and peculiar habit set it well apart. This is sometimes re- 

 garded as a transition group between the preceding alliances 

 and the Centrospermales. In any event, it may be regarded 

 as fairly associated with the latter. 



XIV. Centrospermaees.* — This includes Chenopodia- 

 ceae, Amarantaceae, Xyctaginaceae, Batidaceae, Cynocramba- 

 ceae, Phytolaccaceao, Aizoaceae, Portnlacaceae, Basellaceae, and 

 Caryophyllaceae, together containing about 3,320 species, the 



* Centrospermae of Engler. 



