MORPHOLOGY OF ANGIOSPERMS. 129 



When a flower has but one stamen it is termed monandrous ; 

 and when there are two, three or many stamens, it is said to be 

 diandrous, triandrous or polyandrous (Fig. 84). The aggregate 

 of stamens in the flower is called the andrcecium. In the Labi- 

 atae there are four stamens arranged in a longer and shorter pair 

 and the stamens are said to be didynamous; in the Cruciferse 

 the flowers possess six stamens, four of which are longer than the 

 other two, and the stamens are described as tetradynamous ; 

 in some plants, as in the Lobeliaceae, Papilionatse, etc., the fila- 

 ments cohere, forming groups (Fig. 82) which are termed mona- 

 delphous, diadelphous, etc. ; in the flowers of the potato the 

 anthers lie close together but are not united, forming apparently 

 a continuous ring or band around the pistil, when they are said 

 to be connivent; in the tubular flowers of the Compositse the 

 anthers are united, forming a closed ring, and the stamens are 

 spoken of as syngenesioxjs (Fig. 82, ^) ; in many. of the Cucnr- 

 bitacece the filaments and anthers both are confluent ; in the flowers 

 of the Orchidacese the stamens are borne upon the pistil and are 

 said to be GYNANDROus (Fig. 133). 



Floral Envelopes. — As their name indicates the floral 

 envelopes occupy the outermost or lowest position in the arrange- 

 ment of the parts of the flower. In the bud condition they protect 

 the essential elements, and in the expanded flower are considered 

 to play an important role in securing pollination through the 

 visitation of insects. The floral envelopes are made up generally 

 of two kinds of leaves, petals and sepals (Fig. 83). 



The PETALS form a circle which surrounds the andrcecium. 

 They are as a rule quite bright and attractive, being frequently 

 highly colored, as in the rose. Fuchsia, violet, etc., and are known 

 collectively as the corolla. 



The SEPALS form the next and lowermost circle. They are 

 usually green and leaf-like, as in the rose and carnation, and 

 together constitute the calyx. Sometimes the corolla and calyx 

 are spoken of together as the perianth, although strictly speak- 

 ing the term has a more special application, and is used mostly in 

 speaking of the sepals and petals of monocotyledonous flowersj 

 these parts being much alike and not distinguishable, s^ve in posi- 

 tion, as in certain Hlies (Fig. 123). 



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