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 moiwcolyledones 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- 

 florcB, 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 



.4. Cross-section of the stum of an oak true tliirt\--sevcn years old, showing the 

 annual rings. rin. the niednllary rays; ni. the iiith (nn^dulla). B. Cretss-section 

 of tlie stem of a palm tree, ,sln.^\'in>,' llie seattered Inmdles. 



cross-section (jf tlic stem of a jiahii (lig. 407), or li\' the arrange- 

 ment of the Ijundles in the corn stem (lig. 57). Tluis a single 

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



