CLASSIFICATION I3 



The Arrangement of the Flowers. 



By inflorescence is meant either the arrangement of the flowers 

 on a plant or the flower-cluster itself. A flower is terminal when 

 at the summit of a stem or branch; axillary, when in the axil of 

 a leaf, as in most mints. A peduncle, or flower-stalk, is the stalk 

 either of a solitary flower or of a flower-cluster. A pedicel is the 

 ultimate branchlet of a cluster, supporting a single flower. 



Bracts are small leaves occurring in a flower-cluster below the 

 calyx. Sometimes they are very small and scale-like, sometimes 

 colored. When several bracts encircle a flower or head of flowers, 

 they are collectively called an involucre, as in Eriogonum and in 

 the Sunflower. In the Nuttall Dogwood the involucre is so showy 

 that its bracts are often mistaken for petals. Involucres are 

 often cup-shaped and resemble calyxes. The more common types 

 of inflorescence are explained in the figures. 



Types of Inflorescence. — I. A raceme (note the stalked flowers) ; 

 b, bract; p, pedicel. 2. A spike (flowers sessile). 3. A panicle (flower6 

 scattered). 4. An umbel. 5. A head. 



CLASSIFICATION AND THE USE OF KEYS. 



For purposes of convenience, if for no other reason, it is well 

 to have the multitudinous forms of plant life classified according 

 to some established system. They are more conveniently dis- 

 cussed and comprehended when those individuals which are most 

 alike are brought together under one name. This elementary 

 unit, or group of individuals, all of which are of the same kind, 

 is the species of the systematic botanist. Thus, all of the in- 

 dividuals of Yellow Pine are of one species, the Yellow or 

 ponderosa species of Pine, while all of the individuals of the 

 Sugar Pine belong to the Sugar or lambertiana species. 



Again, it is convenient to have brought together those species 

 which are most alike. This larger group, comprising several or 

 often many similar but distinct species, is the genus (plural 

 genera). All species of Pine, be they Yellow or Sugar or any 

 other kind of Pine, belong to the Pine genus, written Pinus in 

 the Latin form; the species of Fir belong to another genus, 



