CLASSIFICATION OF PHENOGAMS. 41 



present in any one flower, but sucli as are 

 present fall under this rule. Thus a lily has 

 six sepals, six stamens, and a three-lobed 

 pistil. Exogens, on the contrary, never have 

 the parts of their flowers in threes but usu- 

 ally in fives or multiples of five. Aside 

 from these differences between endogens and 

 exogens, there is a nearly constant distinc- 

 tion in the leaves. In the endogens the 

 veins in the leaf are not usually distinct, 

 but when conspicuous they are seen to run 

 parallel to the midrib, — they are parallel- 

 veined. The leaves are usually long and 

 narrow like those of rushes, lilies, and 

 grasses, and their margins are not notched. 

 There are some exceptions, the most promi- 

 nent being the leaves of smilax, and of the 

 trilliums or wake-robins. Most of the leaves 

 of exogens have netted veins, although the 

 pinks and some others have not. 



The Classification of Flowering Plants, 



There is no science in which the arrange- 

 ment of objects into a series of subordinated 

 groups is so thoroughly and minutely worked 

 out as in botany. A knowledge of the 

 methods by which botanists classify plants 

 is of vital importance to one who under- 



