FLORAL ENVELOPES. 41 



327. There is no other essential difference between the 

 calyx and corolla. Therefore, when a plant has but one floral 

 envelope, that one is calyx, whatever may be its colour or 

 degree of developement. 



328. It is necessary, however, to be aware, that sometimes 

 the calyx is reduced to a mere rim, either in consequence 

 of lateral compression, as in the pappus (aigrette, Fr.) of many 

 Composite, or from other unknown causes, as in some 

 Acanthacese. 



329. If the floral envelopes are of such a nature that it 

 is not obvious whether they consist of both calyx and corolla, 

 or of calyx only, they receive the name of periantMum or 

 perigonium. 



330. Plants have frequently no floral envelopes ; in that 

 case flowers are said to be naked or achlamydeous. 



331. When the floral envelopes are deciduous, they fall from 

 the peduncle, as leaves from a branch, by means of an arti- 

 culation ; if they are persistent, it is because no articulation 



exists. 



332. When the margins of floral envelopes are united, the 

 part where the union has taken place is called the tube, and 

 that where they are separate is named the limb. It fre- 

 quently happens that in the calyx an articulation forms be- 

 tween the limb and the tube. 



333. Botanists generally consider that the tube of the calyx 

 is invariably formed by the union of the margins of the sepals. 

 It is, however, probable that it is in some cases a mere dila- 

 tation and expansion of the pedicel itself, as in Eschscholtzia. 



334. When the calyx and corolla are readily distinguish- 

 able from each other, they exhibit the following peculia- 

 rities : 



335. The calyx consists of two or more divisions, usually 

 green, called sepals, which are either distinct, when a calyx is 

 said to be polysepalous ; or which unite by their margins in a 

 greater or less degree, when it is called monosepalous, gamose- 

 palous, or monophyttous. 



