THE MONOCOTYLEDONS 397 



(as, for example, among the orchids, the legumes, the snap- 

 dragons, the mints, etc.). While there is generally an upward 

 evolution of flowers, especially when insect-pollinated, there are 

 in some groups numerous illustrations of floral degeneration. 



THE CLASSIFICATION OF THE ANG-IO SPERMS 



369. The classification of the angiosperms. 1 The subdivision 

 Angiospermce contains two classes : 



CLASS I. The monocotyledons, or Monocotyledonece, with an embryo 



having a single cotyledon and a lateral growing point. 

 CLASS II. The dicotyledons, or Dicotyledone.ee, with an embryo having 



generally two cotyledons and a terminal growing point. 

 SUB-CLASS 1. The Archichlamydece (meaning primitive floral envel- 

 opes), in which the perianth is wanting, or, if pres- 

 ent, has its parts entirely separate from one another. 

 SUB-CLASS 2. The Metaclilamydeaz (meaning later floral envelopes), or 

 Sympetalce, in which the petals are united or borne 

 on tubular, cup-like, or other forms of zonal out- 

 growths from the receptacle (Sec. 152). 



370. The monocotyledons. Besides having the single coty- 

 ledon in the embryo, this group is distinguished from the dicoty- 

 ledons by having a stem structure, with scattered fibro-vascular 

 bundles, instead of a cyclic arrangement. Consequently there 

 can be no development of a central shaft of wood surrounded 

 by a cylinder of bast, with a cambium tissue lying between the 

 two, as is commonly found in the larger dicotyledons. The leaves 

 are generally closed (parallel) veined instead of open (netted) 

 veined, and rarely notched, which means that their fibro-vascular 

 bundles come together at the tip or along the edge of the leaf, 

 instead of ending freely as they do in the dicotyledons. The 

 parts of the flower are generally in three or multiples of three. 



1 The most generally accepted classification of the angiosperms is that of 

 Engler, presented in the Syllabus der Pflanzenfamilien, 1907. A brief state- 

 ment of the chief features of this system will be found in Coulter and Cham- 

 berlain, Morphology of Angiosperms, 1903. 



