CLASSIFICATION OF AKCHICIILAMYDEAE 241 



liances, coordinate with the ten series of Monocotyledons. The 

 general sequence of these alliances is based, as in Monocotyle- 

 dons, upon the development of the perianth and of the floral axis, 

 and the arrangement of floral members ; but other characters, 

 chiefly those derived from the ovules, are also used to disen- 

 tangle relationships. Of course there is no real sequence of 

 these twenty-six alliances, for they represent, for the most part, 

 parallel or divergent lines of development. The sequence of 

 presentation is determined in the main by the relative advance- 

 ment of the lower members of each alliance, whose higher mem- 

 bers may or may not have made great advancement and in many 

 directions. Such an assemblage of forms may be conceived of as 

 a tangled thicket, through which certain paths may be more or 

 less evident, but in which no orderly arrangement is apparent. 

 It would be confusing, even were it possible, to discuss the 

 relationships of each of the twenty-six series. They can only 

 be presented as assemblages of families that seem to lie natural, 

 perhaps not so much on account of their common origin as on 

 account of their approximately equal grade of advancement, 

 and hence " form-groups " rather than necessarily genetic 

 groups. 



The following presentation of the alliances of Arehichlaniy- 

 deae is largely based upon Engier's " Uebersicht liber die Unter- 

 abteilungen, Klassen, Reihen, Unterreihen, und Familien der 

 Embryophyta siphonogama," published in Engler and Prantl's 

 Die Naturlichen Pflanzen familien in 1807 (Lieferung 105). 



The first twelve alliances are especially puzzling. Among 

 them are evidently the most primitive forms in floral structure. 

 They also include the chalazogamic forms, and ovules whose 

 structure is unusual among Angiosperms. The families are 

 practically those that were disposed of by Eichler as Amen- 

 tiferae, together with miscellaneous groups of uncertain affinity. 

 That the so-called Amentiferae or Amentaceae represented a 

 heterogeneous assemblage of forms has long been evident. It is 

 a question whether Engier's splitting up into alliances has not 

 been excessive in this part of his scheme, certain morphological 

 characters sometimes being used that may not prove to be of 

 first importance. In any event, the splitting up will serve to 

 keep apart distinct groups until they can lie recombined natu- 

 rally. There is no region of the Archichlamydeae which has 



