Trrr.s of Neiv York Sfdtc 19 



(b) The vascular hiuullcs of monocotyledons are scattered in 

 the stem; those of tlie dicotyledons are arranged in a ring, or the 

 stem contains a vascular cylinder enclosing a pith. 



(c) The leaves of the monocotyledons possess closed venation, 

 that is, the veins do not end blindly in the margin which, as a 

 result, is entire ; dicotyledons possess leaves with open venation 

 and the margin is often dissected. 



(d) The flowers of the monocotyledons are chiefly 3-merous: 

 those of the dicotyledons are predominately 4- or 5-merous. 



Formerly monocotyledons were believed to be more primitive 

 because of the greater simplicity of their floral structure. How- 

 ever, modern science has demonstrated that dicotyledons are of 

 more ancient origin and that monocotyledons undoubtedly arose 

 from them as an aberrant off-shoot in comparatively recent times. 



The monocotyledons number some 25,000 species and are ar- 

 ranged in ten orders which are grouped in four series. The 

 larger division, the dicotyledons, embraces thirty-four orders, 

 some of which are represented wholly by herbaceous forms, 

 while others consist wholly of woody plants or of both woody 

 and herbaceous species. For convenience the first twenty-six orders 

 of dicotyledons are sometimes listed as Archichlamydeae and in- 

 clude those forms which have either no petals (Apetalae), or 

 petals entirely separate from one another (P oly petal ae), a con- 

 dition of the perianth (chlamys) which is conceded to be prim- 

 itive. The remaining eight orders are characterized by a 

 gamopetalous corolla and are included among the Sympetalae. 



Gross flower characteristics usually distinguish the orders 

 while minor floral characters are used to separate families and 

 genera. An order may contain but one family or — as is gen- 

 erally the case in the large tropical orders — a number of families. 

 Order names end in the Latin feminine plural "ales", as for 

 example, the Salicales, Fagcdes, etc. This literally signifies 

 "plant families related to the willow family," etc. 



Family names end in '^aceae", which is the feminine plural 

 of the Latin suffix aceus, meaning "like or related to". The 

 family name is really an adjective agreeing with the understood 

 name "Plantae", as Plantae Fagaceae, Plantae Oleaceae, etc. 

 Family names are commonly coined by prolonging the name of 

 a genus of the group taken as a representative of it. For example, 

 Fagus is a genus belonging to the Fagaceae, Acer to the Acer- 

 aceae, etc. Some familv names have a different origin which 



