490 



CLASSIFICATION OF ANGIOSPERMS. 



or order Liliales. The various orders unite to make up the class, 

 and the classes unite to form a group. 



936. Variations in usage of the terms class, order, etc. 

 Thus, according to the system of classification adopted by some, 

 the angiosperms form a group. The group angiosperms is then 

 divided into two classes, the monocotyledones and dicotyledones. 

 (It should be remembered that all systematists do not agree in 

 assigning the same grade and limits to the classes, subclasses, 

 etc. For example, some treat of the angiosperms as a class, 

 and the monocotyledons and dicotyledons as subclasses; while 

 others would divide the monocotyledons and dicotyledons into 

 classes, instead of treating each one as a class or as a subclass. 

 Systematists differ also in usage as to the termination .of the 

 ordinal name; for example, some use the word Liliales for Lilii- 

 florce, in writing of the order.) 



937. Monocotyledones. In the monocotyledons there is a 

 single cotyledon on the embryo; the leaves are parallel veined; 

 the parts of the flower are usually in threes; endosperm is usu- 

 ally present in the seed; the vascular bundles are usually closed, 

 and are scattered irregularly through the stem as shown by a 



rm 



Fig. 497. 



A. Cross-section of the stem of an oak tree thirty-seven years old, showing the 

 annual rings. rm, the medullary rays; m, the pith (medulla). B. Cross-section 

 of the stem of a palm tree, showing the scattered bundles. 



cross-section of the stem of a palm (fig. 497), or by the arrange- 

 ment of the bundles in the corn stem (fig. 57). Thus a single 

 character is not sufficient to show relationship in the class (nor 



