234 



BOTANY. 



or order Liliiflorce. The various orders unite to make up the 

 class, and the classes unite to form a group. 



381. 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 angio- 

 sperms 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 as the monocotyledons and dicoty- 

 ledons as subclasses; while others would divide the monocoty- 

 ledons; 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 LiliiflorcB, in writing of the order. ) 



382. 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 



A B 



Fig. 204. 

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

 rings, rw, the medullary rays; ;«, the pith (medulla). B. Cross-section of the stem of 

 a palin tree, showing the scattered bundles. 



usually present in the seed; the vascular bundles are usually 

 closed, and are scattered irregularly through the stem as shown 

 by a cross-section of the stem of a palm (fig. 204), or by the 

 arrangement of the bundles in the corn stem (fig. 51). Thus 



