254 MORPHOLOGY OP ANGIOSPERMS 



is much needed ; and the whole series of Ericales deserves atten- 

 tion on account of its possible genetic connections with sonic 

 region of the Archichlamydeae. 



II. Piumulales. — This includes the Myrsinaceae, Priniula- 

 ceae, and Plumbaginaceae, together containing about 850 spe- 

 cies, approximately equally distributed among the three fami- 

 lies. The families are closely associated in structure, but 

 widely separated in geographical distribution, the Myrsinaceae 

 being characteristically tropical trees and shrubs (chiefly Amer- 

 ican), the Primulaceae north temperate and boreal herbs, and 

 the Plumbaginaceae characteristically halophytic herbs and un- 

 dershrubs of salt-beaches and steppes (chiefly Mediterranean 

 and Caspian). That such dissociated families should have so 

 much in common is a strong argument against the older idea 

 that similarity of structure proves common origin. 



The two most characteristic features of the group are the 

 single cycle of stamens opposite the petals, and the unilocular 

 ovary with its " free central placenta " bearing numerous ovules. 

 The single cycle of stamens and its opposition to the petals are 

 explained by the frequent occurrence of rudiments representing 

 an outer abortive cycle. The " free central placenta " of tax- 

 onomists is of course a continuation of the floral axis to bear 

 ovules, and is perhaps the most important morphological char- 

 acter of the series. It is in this group, also, that there has been 

 noted a peculiar origin of the petals, which are said to arise 

 late from the primordia that have already developed the 

 stamens. 



As compared with the Ericales, the Primulales may be re- 

 garded as somewhat more advanced toward the higher Sympeta- 

 lae, but polypetaly still occurs among them, and they give the 

 impression of a somewhat divergent and specialized group. An 

 investigation of the Myrsinaceae will doubtless result in a much 

 clearer understanding of the relationships. 



III. Ebexales. — This includes the Sapotaceae, Ebenaceae, 

 Styracaeeae, and Symploeneeao, together containing nearly 000 

 species, the large families being Sapotaceae with about 380 spe- 

 cies, and Ebenaceae with 275. The group is chiefly developed 

 in the tropics and the species are all shrubs or trees. 



The alliance is particularly puzzling in its affinities, since 

 there is a combination of primitive and advanced characters. 



