EXPLANATION OF TERMS 



LXXIX., where the involucre surrounds what is probably con- 

 sidered a single flower, but what is actually a cluster of ray- and 

 disk-flowers ; also bunch-berry, PI. XVIII. ; where the involucre 

 consists of the four showy white leaves which are usually supposed 

 to be petals, while the greenish centre is actually a cluster of in- 

 conspicuous flowers.) 



A leaf or flower which is set so close in the stem as to show 

 no sign of a separate leaf or flower -stalk, is said to be Sessile. 



A Complete Flower (Fig. 6) is '' that part of a plant which 

 subserves the purpose of producing seed, consisting of stamens 

 and pistils, which are the essential organs, and the calyx and 

 corolla, which are the protecting organs." (Gray.) 



The green outer flower-cup, or outer set of green leaves, 

 which we notice at the base of many flowers, is the Calyx (Fig. 

 6 Ca). At times this part is brightly colored and may be the 

 most conspicuous feature of the flower. 



When the calyx is divided into separate leaves, these leaves 

 are called Sepals. 



The inner flower-cup or the inner set of leaves is the Corolla 

 (Fig. 6, C). 



When the corolla is divided into separate leaves, these leaves 

 are called Petals. 



We can look upon calyx and corolla as the natural tapestry 

 which protects the delicate organs of the flower, and serves as 

 well, in many cases, to attract the attention of passing insects. 

 In some flowers only one of these two parts is present ; in such a 

 case the single cup or set of floral leaves is generally considered to 

 be the calyx. 



The floral leaves may be spoken of collectively as the Peri- 

 anth. This word is used especially in describing members of 

 families where there might be difficulty in deciding as to whether 

 the single set of floral leaves present should be considered calyx 

 or corolla (see Lilies, Pis. LXX. and CXXI.) ; or where the 

 petals and sepals can only be distinguished with difficulty, as 

 with the Orchids. 



The Stamens (Fig. 7) are the fertilizing organs of the flower. 



xxxi 



