ELEMENTS OF STRUCTURAL BOTANY. 85 



case of the umbel and the head, it generally happens 

 that a circle of bracts surrounds the base of the cluster. 

 They are then called, collectively, an involucre, and in 

 tlie case of compound clusters a circle of bractlets is 

 called an involucel. Bracts are often so minute as to be 

 reduced to mere scales. From our definition, it will be 

 evident that the spathe surrounding tlie spadix in 

 Indian Turnip is merely a bract. 



126. It has already been stated that the parts of the 

 flower, equally witli the foliage-leaves, must be regarded 

 as mcdilications of the same structure, and some proofs 

 of this similarity of structure were given. We shall 

 now proceed to consider in detail the variations in form 

 assumed by these organs. 



127. The Calyx. As you are now well aware, this 

 term is applied to the outer circle of floral leaves. These 

 are usually green, but not necessarily so ; in some Ex- 

 ogens, and in nearly all Eudogens, they are of some 

 other colour. Each division (A a calyx is called a se/ial, 

 and if the sepals are entirely distinct from each other, 

 the calyx is lyohjsepalous ; if they are united in any de- 

 gree, it is ffamosejxilous. A calyx is reijidar or irre(jidar, 

 according as the sepals are of the same or difi'erent 

 shape and size. 



128. In a gamosepalous calyx, if the sepals are not 

 united to the very top, the free portions are known as 

 (uhf.r-tteth, or, taken collectively; as the liinh of the 

 calyx. The united portion, especially if long, as in 

 "Willow-herb, is called the calyx-tnle, and the entrance 

 to the tube its i Id out. In many plants, particularly 

 those of the Composite Family, the limb of the calyx 

 consists merely of a circle of bristles or soft hairs, 



