CHAPTEE XXV 



MONOCOTYLEDONS AND DICOTYLEDONS 



2iU. Contrasting characters. — The two great groui^s of 

 Angiosperms arc quite distinct, and there is usually no dif- 

 ficulty in recognizing them. The monocotyledons are 

 usually regarded as the older and the simpler forms, and 

 are represented by about twenty thousand species. The 

 Dicotyledons are much more almndant and diversified, con- 

 taining about eighty thousand species, and form the domi- 

 nant vegetation almost everywhere. 

 The chief contrasting characters 

 may be stated as follows : 



Moyiocotyledons. — (1) Embryo 

 with terminal cotyledon and lat- 

 eral stem-tip. This character is 

 practically without exception. 



{'i) Vascular bundles of stem 



scattered (Fig. 33'.'). This means 



that there is no annual increase in 



tlie diameter of the woody stems, 



and no extensive l)ran('hing, but 



to this there are some exceptions. 



(3) Leaf veins forming a closed 



system (Fig. 333, iigure to left). 



As a rule there is an evident set 



of veins wliii-h run approximately parallel, and intricately 



branching between them is a system of minute veinlets not 



readily seen. The vein system does not end freely in the 



Y\u. 8;«. Rortinn of .sU'm of 

 corn, Hliowiiii^^ tlir scattcrrd 

 bundles, iiidlcatcil liy black 

 dots iu cross-f^eetioii, and by 

 lines in lonLntudinul si-'ction. 

 —From •■I'liuit Ui/laiifnis.'^ 



