XXIV 



INTRODUCTION 



The Flower is a branch bearing leaves modified so as to 

 assist in the jjroduction of seed, and generally crowded together 

 on the expanded apex of the pedicel, or flower-stalk, which is 

 termed the receptacle or thalanms. As much of the classification 

 of plants is based upon the characters of the flower, a knowledge 

 of its structure is indispensable to the student. A typical flower 

 has four kinds of floral leaves, sepals^ petals^ sta?nenSy and carpels. 

 The sepals collectively form the caly'x (Greek for a cup), and the 

 petals constitute the corolla ("little crown"). The calyx and 

 corolla together are called the perianth (Greek peri-^ round, 

 anthos^ a flower), or floral envelopes whilst the stamens and 

 carpels are called the essential organs^ because seed cannot be 

 formed if they are absent. If both calyx and corolla are present in 

 the same flower, as in the Buttercup, in which flower the five 



Section of a flower. 



Asymmetric flower of Valerian. 



sepals are green and the petals golden, the flower is termed 

 co'Hplete ; but if one of these envelopes is absent, as in the Marsh- 

 marigold, the flower is iricomplete. Incomplete flowers are mono- 

 chlamydeous (^Greek monos^ one, chlamys^ a cloak) if, as in this 

 case, they have one envelope ; achlaniydeous if, as in the Ash, they 

 have neither calyx nor corolla. If both stamens and carpels 

 occur in the same flower it is termed perfect ; if only one class of 

 essential organs is present the flower is imperfect^ and stamitiate or 

 larpellate as the case may be. Plants with imperfect flowers may 

 either be monoecious (Greek monos, one, oikos, a house), where, as 

 in the Hazel, the staminate and carpellate flowers are on the same 

 plant ; or dioecious^ where, as in Willows and Poplars, they are on 

 different individuals. Where neither stamens nor carpels are 

 present, as in the outer florets of the blue Cornflower, or the outer 

 flowers in the cluster of the Guelder Rose, the flower is tieuter. 



