CLASSIFICATION OF MONOCOTYLEDONS 231 



with the preceding alliances, is that the bract does not eusheath 

 a whole flower-cluster but individual flowers. It is this charac- 

 teristic bract (glume, palet) that gives name to the alliance. 

 The lodicules of Gramineae and certain hairs and bracts of 

 Cvperaceae are regarded by some as representing a perianth. 

 Even if this doubtful claim be allowed, such a perianth is 

 better regarded as one that is very primitive rather than re- 

 duced. 



The primitive character of Glumales is indicated by the 

 characters given above, but contrasted with the Helobiales it is 

 a rigid group that has not advanced far in floral development, 

 but has proved to be a remarkably successful type of vegeta- 

 tion. Moreover, it is the primitive group of Monocotyledons 

 that seems to have been the first to establish itself upon the 

 drier and more diversified land surface, and this fact may hold 

 some relation to its structural stability and its great display of 

 species. Evidence of its aquatic origin may be obtained not 

 only from the numerous hydrophytic forms, but also from ana- 

 tomical characters that relate it to Helobiales and Pandanales 

 rather than to the terrestrial alliances. 



Pandanales, Helobiales, and Glumales are the only three 

 alliances of Monocotyledons that include the most primitive 

 type of monocotyledonous floral structure. Their possible ge- 

 netic relation to one another is entirely obscure, and in their 

 present display they seem to emerge from the beginnings of the 

 history of Monocotyledons as independent lines. The remain- 

 ing seven alliances are either derived from these three, or their 

 primitive members have disappeared. 



IV. PALM ALES. * The palms are the chief representatives 

 of monocotyledonous trees, and are characteristic of all tropical 

 regions. The single family Palmaceae includes about 150 gen- 

 era and 1,100 species, though these numbers will doubtless be 

 much increased when the palms are studied in their habitats. 

 A knowledge of the essential morphology of this group is also 

 much to be desired. 



A perianth is always present, although it is very " rudimen- 

 tary " and hence doubtful in Phytelephas and Coryphanthe, 

 but it is not differentiated into a distinct calvx and corolla. 



* PRIXCIPES of Engler. 

 16 



