NATURAL ARRANGEMENT 

 OF PLANTS 



Class I 



DICOTYLEDONOUS OR EXOGENOUS PLANTS 



r T*HE characteristics by which plants belonging to this class 

 *- may be distinguished from members of the less extensive 

 class, Monocotyledons, are mainly as follows : 



The seeds are composed of two lobes or cotyledons, which enclose 

 the plumule, or embryo of the future plant. As germination com- 

 mences, the plumule lengthens downwards into a root, called in its 

 early stage a radicle. At the same time the upper extremity 

 lengthens into a stem, which is composed of bark, woody fibre, 

 spiral vessels, cellular tissue, and a central column of pith. 

 The stem increases in diameter by deposits beneath the bark, but 

 outside the existing fibre. Hence the plants belonging to this 

 class are called Exogenous (increasing by additions on the out- 

 side). In all trees and shrubs of this class the wood is arranged in 

 concentric layers, the hardest part being nearest the pith. The 

 leaves are netted-veined, as opposed to the parallel-veined leaves 

 of Monocotyledons. (Compare the leaves of a common primrose 

 with those of a lily of the valley.) 



The parts of the flowers are usually arranged in fours, fives, or 

 some multiple of those numbers. 



With a little observation the student will quickly come to be able 

 to recognize the essential characteristics of Dicotyledons and Mono- 

 cotyledons, whose general aspects are really very distinct. 



Sub-Class I 



THALAM I FLORAE 



Flowers furnished with calyx and corolla ; petals distinct, inserted 

 into the receptacle or thalamus ; stamens inferior, i.e. springing from 

 below the base of the ovary. 



